diff --git a/backend/app/services/dashboard_service.py b/backend/app/services/dashboard_service.py
index c1ef4fc..3be2ccc 100644
--- a/backend/app/services/dashboard_service.py
+++ b/backend/app/services/dashboard_service.py
@@ -103,7 +103,7 @@ class DashboardService:
             try:
                 result = await self.db.execute(
                     select(func.coalesce(func.sum(TrainingSession.duration_seconds), 0))
-                    .where(TrainingSession.status == 'COMPLETED')
+                    .where(TrainingSession.status == 'completed')  # 修复: 使用小写
                 )
                 training_hours = (result.scalar() or 0) / 3600
             except Exception as e: