diff --git a/api/tests/unit_tests/services/test_account_service.py b/api/tests/unit_tests/services/test_account_service.py
new file mode 100644
index 0000000000..c71a2797c0
--- /dev/null
+++ b/api/tests/unit_tests/services/test_account_service.py
@@ -0,0 +1,571 @@
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from configs import dify_config
+from models.account import Account
+from services.account_service import AccountService
+from services.errors.account import (
+    AccountLoginError,
+    AccountNotFoundError,
+    AccountPasswordError,
+    AccountRegisterError,
+    CurrentPasswordIncorrectError,
+)
+
+
+class AccountServiceTestDataFactory:
+    """Factory class for creating test data and mock objects for account service tests."""
+
+    @staticmethod
+    def create_account_mock(
+        account_id: str = "user-123",
+        email: str = "test@example.com",
+        name: str = "Test User",
+        status: str = "active",
+        password: str = "hashed_password",
+        password_salt: str = "salt",
+        interface_language: str = "en-US",
+        interface_theme: str = "light",
+        timezone: str = "UTC",
+        **kwargs,
+    ) -> MagicMock:
+        """Create a mock account with specified attributes."""
+        account = MagicMock(spec=Account)
+        account.id = account_id
+        account.email = email
+        account.name = name
+        account.status = status
+        account.password = password
+        account.password_salt = password_salt
+        account.interface_language = interface_language
+        account.interface_theme = interface_theme
+        account.timezone = timezone
+        account.last_active_at = MagicMock()
+        account.initialized_at = None
+        for key, value in kwargs.items():
+            setattr(account, key, value)
+        return account
+
+    @staticmethod
+    def create_tenant_join_mock(
+        tenant_id: str = "tenant-456",
+        account_id: str = "user-123",
+        current: bool = True,
+        role: str = "normal",
+        **kwargs,
+    ) -> MagicMock:
+        """Create a mock tenant account join record."""
+        tenant_join = MagicMock()
+        tenant_join.tenant_id = tenant_id
+        tenant_join.account_id = account_id
+        tenant_join.current = current
+        tenant_join.role = role
+        for key, value in kwargs.items():
+            setattr(tenant_join, key, value)
+        return tenant_join
+
+    @staticmethod
+    def create_feature_service_mock(allow_register: bool = True):
+        """Create a mock feature service."""
+        mock_service = MagicMock()
+        mock_service.get_system_features.return_value.is_allow_register = allow_register
+        return mock_service
+
+    @staticmethod
+    def create_billing_service_mock(email_frozen: bool = False):
+        """Create a mock billing service."""
+        mock_service = MagicMock()
+        mock_service.is_email_in_freeze.return_value = email_frozen
+        return mock_service
+
+
+class TestAccountService:
+    """
+    Comprehensive unit tests for AccountService methods.
+
+    This test suite covers all account-related operations including:
+    - Authentication and login
+    - Account creation and registration
+    - Password management
+    - JWT token generation
+    - User loading and tenant management
+    - Error conditions and edge cases
+    """
+
+    @pytest.fixture
+    def mock_db_dependencies(self):
+        """Common mock setup for database dependencies."""
+        with patch("services.account_service.db") as mock_db:
+            mock_db.session.add = MagicMock()
+            mock_db.session.commit = MagicMock()
+            yield {
+                "db": mock_db,
+            }
+
+    @pytest.fixture
+    def mock_password_dependencies(self):
+        """Mock setup for password-related functions."""
+        with (
+            patch("services.account_service.compare_password") as mock_compare_password,
+            patch("services.account_service.hash_password") as mock_hash_password,
+            patch("services.account_service.valid_password") as mock_valid_password,
+        ):
+            yield {
+                "compare_password": mock_compare_password,
+                "hash_password": mock_hash_password,
+                "valid_password": mock_valid_password,
+            }
+
+    @pytest.fixture
+    def mock_external_service_dependencies(self):
+        """Mock setup for external service dependencies."""
+        with (
+            patch("services.account_service.FeatureService") as mock_feature_service,
+            patch("services.account_service.BillingService") as mock_billing_service,
+            patch("services.account_service.PassportService") as mock_passport_service,
+        ):
+            yield {
+                "feature_service": mock_feature_service,
+                "billing_service": mock_billing_service,
+                "passport_service": mock_passport_service,
+            }
+
+    @pytest.fixture
+    def mock_db_with_autospec(self):
+        """
+        Mock database with autospec for more realistic behavior.
+        This approach preserves the actual method signatures and behavior.
+        """
+        with patch("services.account_service.db", autospec=True) as mock_db:
+            # Create a more realistic session mock
+            mock_session = MagicMock()
+            mock_db.session = mock_session
+
+            # Setup basic session methods
+            mock_session.add = MagicMock()
+            mock_session.commit = MagicMock()
+            mock_session.query = MagicMock()
+
+            yield mock_db
+
+    def _setup_smart_db_query_mock(self, mock_db, query_results):
+        """
+        Smart database query mock that responds based on model type and query parameters.
+
+        Args:
+            mock_db: Mock database session
+            query_results: Dict mapping (model_name, filter_key, filter_value) to return value
+                          Example: {('Account', 'email', 'test@example.com'): mock_account}
+        """
+
+        def query_side_effect(model):
+            mock_query = MagicMock()
+
+            def filter_by_side_effect(**kwargs):
+                mock_filter_result = MagicMock()
+
+                def first_side_effect():
+                    # Find matching result based on model and filter parameters
+                    for (model_name, filter_key, filter_value), result in query_results.items():
+                        if model.__name__ == model_name and filter_key in kwargs and kwargs[filter_key] == filter_value:
+                            return result
+                    return None
+
+                mock_filter_result.first.side_effect = first_side_effect
+
+                # Handle order_by calls for complex queries
+                def order_by_side_effect(*args, **kwargs):
+                    mock_order_result = MagicMock()
+
+                    def order_first_side_effect():
+                        # Look for order_by results in the same query_results dict
+                        for (model_name, filter_key, filter_value), result in query_results.items():
+                            if (
+                                model.__name__ == model_name
+                                and filter_key == "order_by"
+                                and filter_value == "first_available"
+                            ):
+                                return result
+                        return None
+
+                    mock_order_result.first.side_effect = order_first_side_effect
+                    return mock_order_result
+
+                mock_filter_result.order_by.side_effect = order_by_side_effect
+                return mock_filter_result
+
+            mock_query.filter_by.side_effect = filter_by_side_effect
+            return mock_query
+
+        mock_db.session.query.side_effect = query_side_effect
+
+    def _assert_database_operations_called(self, mock_db):
+        """Helper method to verify database operations were called."""
+        mock_db.session.commit.assert_called()
+
+    def _assert_database_operations_not_called(self, mock_db):
+        """Helper method to verify database operations were not called."""
+        mock_db.session.commit.assert_not_called()
+
+    def _assert_exception_raised(self, exception_type, callable_func, *args, **kwargs):
+        """Helper method to verify that specific exception is raised."""
+        with pytest.raises(exception_type):
+            callable_func(*args, **kwargs)
+
+    # ==================== Authentication Tests ====================
+
+    def test_authenticate_success(self, mock_db_dependencies, mock_password_dependencies):
+        """Test successful authentication with correct email and password."""
+        # Setup test data
+        mock_account = AccountServiceTestDataFactory.create_account_mock()
+
+        # Setup smart database query mock
+        query_results = {("Account", "email", "test@example.com"): mock_account}
+        self._setup_smart_db_query_mock(mock_db_dependencies["db"], query_results)
+
+        mock_password_dependencies["compare_password"].return_value = True
+
+        # Execute test
+        result = AccountService.authenticate("test@example.com", "password")
+
+        # Verify results
+        assert result == mock_account
+        self._assert_database_operations_called(mock_db_dependencies["db"])
+
+    def test_authenticate_account_not_found(self, mock_db_dependencies):
+        """Test authentication when account does not exist."""
+        # Setup smart database query mock - no matching results
+        query_results = {("Account", "email", "notfound@example.com"): None}
+        self._setup_smart_db_query_mock(mock_db_dependencies["db"], query_results)
+
+        # Execute test and verify exception
+        self._assert_exception_raised(
+            AccountNotFoundError, AccountService.authenticate, "notfound@example.com", "password"
+        )
+
+    def test_authenticate_account_banned(self, mock_db_dependencies):
+        """Test authentication when account is banned."""
+        # Setup test data
+        mock_account = AccountServiceTestDataFactory.create_account_mock(status="banned")
+
+        # Setup smart database query mock
+        query_results = {("Account", "email", "banned@example.com"): mock_account}
+        self._setup_smart_db_query_mock(mock_db_dependencies["db"], query_results)
+
+        # Execute test and verify exception
+        self._assert_exception_raised(AccountLoginError, AccountService.authenticate, "banned@example.com", "password")
+
+    def test_authenticate_password_error(self, mock_db_dependencies, mock_password_dependencies):
+        """Test authentication with wrong password."""
+        # Setup test data
+        mock_account = AccountServiceTestDataFactory.create_account_mock()
+
+        # Setup smart database query mock
+        query_results = {("Account", "email", "test@example.com"): mock_account}
+        self._setup_smart_db_query_mock(mock_db_dependencies["db"], query_results)
+
+        mock_password_dependencies["compare_password"].return_value = False
+
+        # Execute test and verify exception
+        self._assert_exception_raised(
+            AccountPasswordError, AccountService.authenticate, "test@example.com", "wrongpassword"
+        )
+
+    def test_authenticate_pending_account_activates(self, mock_db_dependencies, mock_password_dependencies):
+        """Test authentication for a pending account, which should activate on login."""
+        # Setup test data
+        mock_account = AccountServiceTestDataFactory.create_account_mock(status="pending")
+
+        # Setup smart database query mock
+        query_results = {("Account", "email", "pending@example.com"): mock_account}
+        self._setup_smart_db_query_mock(mock_db_dependencies["db"], query_results)
+
+        mock_password_dependencies["compare_password"].return_value = True
+
+        # Execute test
+        result = AccountService.authenticate("pending@example.com", "password")
+
+        # Verify results
+        assert result == mock_account
+        assert mock_account.status == "active"
+        self._assert_database_operations_called(mock_db_dependencies["db"])
+
+    # ==================== Account Creation Tests ====================
+
+    def test_create_account_success(
+        self, mock_db_dependencies, mock_password_dependencies, mock_external_service_dependencies
+    ):
+        """Test successful account creation with all required parameters."""
+        # Setup mocks
+        mock_external_service_dependencies["feature_service"].get_system_features.return_value.is_allow_register = True
+        mock_external_service_dependencies["billing_service"].is_email_in_freeze.return_value = False
+        mock_password_dependencies["hash_password"].return_value = b"hashed_password"
+
+        # Execute test
+        result = AccountService.create_account(
+            email="test@example.com",
+            name="Test User",
+            interface_language="en-US",
+            password="password123",
+            interface_theme="light",
+        )
+
+        # Verify results
+        assert result.email == "test@example.com"
+        assert result.name == "Test User"
+        assert result.interface_language == "en-US"
+        assert result.interface_theme == "light"
+        assert result.password is not None
+        assert result.password_salt is not None
+        assert result.timezone is not None
+
+        # Verify database operations
+        mock_db_dependencies["db"].session.add.assert_called_once()
+        added_account = mock_db_dependencies["db"].session.add.call_args[0][0]
+        assert added_account.email == "test@example.com"
+        assert added_account.name == "Test User"
+        assert added_account.interface_language == "en-US"
+        assert added_account.interface_theme == "light"
+        assert added_account.password is not None
+        assert added_account.password_salt is not None
+        assert added_account.timezone is not None
+        self._assert_database_operations_called(mock_db_dependencies["db"])
+
+    def test_create_account_registration_disabled(self, mock_external_service_dependencies):
+        """Test account creation when registration is disabled."""
+        # Setup mocks
+        mock_external_service_dependencies["feature_service"].get_system_features.return_value.is_allow_register = False
+
+        # Execute test and verify exception
+        self._assert_exception_raised(
+            Exception,  # AccountNotFound
+            AccountService.create_account,
+            email="test@example.com",
+            name="Test User",
+            interface_language="en-US",
+        )
+
+    def test_create_account_email_frozen(self, mock_db_dependencies, mock_external_service_dependencies):
+        """Test account creation with frozen email address."""
+        # Setup mocks
+        mock_external_service_dependencies["feature_service"].get_system_features.return_value.is_allow_register = True
+        mock_external_service_dependencies["billing_service"].is_email_in_freeze.return_value = True
+        dify_config.BILLING_ENABLED = True
+
+        # Execute test and verify exception
+        self._assert_exception_raised(
+            AccountRegisterError,
+            AccountService.create_account,
+            email="frozen@example.com",
+            name="Test User",
+            interface_language="en-US",
+        )
+        dify_config.BILLING_ENABLED = False
+
+    def test_create_account_without_password(self, mock_db_dependencies, mock_external_service_dependencies):
+        """Test account creation without password (for invite-based registration)."""
+        # Setup mocks
+        mock_external_service_dependencies["feature_service"].get_system_features.return_value.is_allow_register = True
+        mock_external_service_dependencies["billing_service"].is_email_in_freeze.return_value = False
+
+        # Execute test
+        result = AccountService.create_account(
+            email="test@example.com",
+            name="Test User",
+            interface_language="zh-CN",
+            password=None,
+            interface_theme="dark",
+        )
+
+        # Verify results
+        assert result.email == "test@example.com"
+        assert result.name == "Test User"
+        assert result.interface_language == "zh-CN"
+        assert result.interface_theme == "dark"
+        assert result.password is None
+        assert result.password_salt is None
+        assert result.timezone is not None
+
+        # Verify database operations
+        mock_db_dependencies["db"].session.add.assert_called_once()
+        added_account = mock_db_dependencies["db"].session.add.call_args[0][0]
+        assert added_account.email == "test@example.com"
+        assert added_account.name == "Test User"
+        assert added_account.interface_language == "zh-CN"
+        assert added_account.interface_theme == "dark"
+        assert added_account.password is None
+        assert added_account.password_salt is None
+        assert added_account.timezone is not None
+        self._assert_database_operations_called(mock_db_dependencies["db"])
+
+    # ==================== Password Management Tests ====================
+
+    def test_update_account_password_success(self, mock_db_dependencies, mock_password_dependencies):
+        """Test successful password update with correct current password and valid new password."""
+        # Setup test data
+        mock_account = AccountServiceTestDataFactory.create_account_mock()
+        mock_password_dependencies["compare_password"].return_value = True
+        mock_password_dependencies["valid_password"].return_value = None
+        mock_password_dependencies["hash_password"].return_value = b"new_hashed_password"
+
+        # Execute test
+        result = AccountService.update_account_password(mock_account, "old_password", "new_password123")
+
+        # Verify results
+        assert result == mock_account
+        assert mock_account.password is not None
+        assert mock_account.password_salt is not None
+
+        # Verify password validation was called
+        mock_password_dependencies["compare_password"].assert_called_once_with(
+            "old_password", "hashed_password", "salt"
+        )
+        mock_password_dependencies["valid_password"].assert_called_once_with("new_password123")
+
+        # Verify database operations
+        self._assert_database_operations_called(mock_db_dependencies["db"])
+
+    def test_update_account_password_current_password_incorrect(self, mock_password_dependencies):
+        """Test password update with incorrect current password."""
+        # Setup test data
+        mock_account = AccountServiceTestDataFactory.create_account_mock()
+        mock_password_dependencies["compare_password"].return_value = False
+
+        # Execute test and verify exception
+        self._assert_exception_raised(
+            CurrentPasswordIncorrectError,
+            AccountService.update_account_password,
+            mock_account,
+            "wrong_password",
+            "new_password123",
+        )
+
+        # Verify password comparison was called
+        mock_password_dependencies["compare_password"].assert_called_once_with(
+            "wrong_password", "hashed_password", "salt"
+        )
+
+    def test_update_account_password_invalid_new_password(self, mock_password_dependencies):
+        """Test password update with invalid new password."""
+        # Setup test data
+        mock_account = AccountServiceTestDataFactory.create_account_mock()
+        mock_password_dependencies["compare_password"].return_value = True
+        mock_password_dependencies["valid_password"].side_effect = ValueError("Password too short")
+
+        # Execute test and verify exception
+        self._assert_exception_raised(
+            ValueError, AccountService.update_account_password, mock_account, "old_password", "short"
+        )
+
+        # Verify password validation was called
+        mock_password_dependencies["valid_password"].assert_called_once_with("short")
+
+        # ==================== User Loading Tests ====================
+
+        def test_load_user_success(self, mock_db_dependencies):
+            """Test successful user loading with current tenant."""
+            # Setup test data
+            mock_account = AccountServiceTestDataFactory.create_account_mock()
+            mock_tenant_join = AccountServiceTestDataFactory.create_tenant_join_mock()
+
+            # Setup smart database query mock
+            query_results = {
+                ("Account", "id", "user-123"): mock_account,
+                ("TenantAccountJoin", "account_id", "user-123"): mock_tenant_join,
+            }
+            self._setup_smart_db_query_mock(mock_db_dependencies["db"], query_results)
+
+            # Mock datetime
+            with patch("services.account_service.datetime") as mock_datetime:
+                mock_now = MagicMock()
+                mock_datetime.now.return_value = mock_now
+                mock_datetime.UTC = "UTC"
+
+                # Execute test
+                result = AccountService.load_user("user-123")
+
+                # Verify results
+                assert result == mock_account
+                assert mock_account.set_tenant_id.called
+
+    def test_load_user_not_found(self, mock_db_dependencies):
+        """Test user loading when user does not exist."""
+        # Setup smart database query mock - no matching results
+        query_results = {("Account", "id", "non-existent-user"): None}
+        self._setup_smart_db_query_mock(mock_db_dependencies["db"], query_results)
+
+        # Execute test
+        result = AccountService.load_user("non-existent-user")
+
+        # Verify results
+        assert result is None
+
+    def test_load_user_banned(self, mock_db_dependencies):
+        """Test user loading when user is banned."""
+        # Setup test data
+        mock_account = AccountServiceTestDataFactory.create_account_mock(status="banned")
+
+        # Setup smart database query mock
+        query_results = {("Account", "id", "user-123"): mock_account}
+        self._setup_smart_db_query_mock(mock_db_dependencies["db"], query_results)
+
+        # Execute test and verify exception
+        self._assert_exception_raised(
+            Exception,  # Unauthorized
+            AccountService.load_user,
+            "user-123",
+        )
+
+        def test_load_user_no_current_tenant(self, mock_db_dependencies):
+            """Test user loading when user has no current tenant but has available tenants."""
+            # Setup test data
+            mock_account = AccountServiceTestDataFactory.create_account_mock()
+            mock_available_tenant = AccountServiceTestDataFactory.create_tenant_join_mock(current=False)
+
+            # Setup smart database query mock for complex scenario
+            query_results = {
+                ("Account", "id", "user-123"): mock_account,
+                ("TenantAccountJoin", "account_id", "user-123"): None,  # No current tenant
+                ("TenantAccountJoin", "order_by", "first_available"): mock_available_tenant,  # First available tenant
+            }
+            self._setup_smart_db_query_mock(mock_db_dependencies["db"], query_results)
+
+            # Mock datetime
+            with patch("services.account_service.datetime") as mock_datetime:
+                mock_now = MagicMock()
+                mock_datetime.now.return_value = mock_now
+                mock_datetime.UTC = "UTC"
+
+                # Execute test
+                result = AccountService.load_user("user-123")
+
+                # Verify results
+                assert result == mock_account
+                assert mock_available_tenant.current is True
+                self._assert_database_operations_called(mock_db_dependencies["db"])
+
+        def test_load_user_no_tenants(self, mock_db_dependencies):
+            """Test user loading when user has no tenants at all."""
+            # Setup test data
+            mock_account = AccountServiceTestDataFactory.create_account_mock()
+
+            # Setup smart database query mock for no tenants scenario
+            query_results = {
+                ("Account", "id", "user-123"): mock_account,
+                ("TenantAccountJoin", "account_id", "user-123"): None,  # No current tenant
+                ("TenantAccountJoin", "order_by", "first_available"): None,  # No available tenants
+            }
+            self._setup_smart_db_query_mock(mock_db_dependencies["db"], query_results)
+
+            # Mock datetime
+            with patch("services.account_service.datetime") as mock_datetime:
+                mock_now = MagicMock()
+                mock_datetime.now.return_value = mock_now
+                mock_datetime.UTC = "UTC"
+
+                # Execute test
+                result = AccountService.load_user("user-123")
+
+                # Verify results
+                assert result is None