diff --git a/backend/app/api/budget.py b/backend/app/api/budget.py
index 087aebb8..35f5fa47 100644
--- a/backend/app/api/budget.py
+++ b/backend/app/api/budget.py
@@ -908,6 +908,9 @@ def check_budget_deviation(
         )
         db.add(alert)
         alerts_generated += 1
+        # 立即 flush：autoflush=False 下，下一次循环的同 KPI 去重查询
+        # (existing_alert) 需看到本次已 add 的行，否则同期间同 KPI 多预算计划会重复告警
+        db.flush()
 
         alerts.append({
             "kpi_id": bp.kpi_id,
diff --git a/backend/tests/test_budget.py b/backend/tests/test_budget.py
index f6916534..55e27569 100644
--- a/backend/tests/test_budget.py
+++ b/backend/tests/test_budget.py
@@ -461,6 +461,34 @@ class TestBudgetDeviationCheck:
                            json={"period": "2026-06", "threshold": 20})
         assert resp.json()["alerts_generated"] == 0
 
+    def test_deviation_check_dedups_same_kpi_multiple_plans(self, client: TestClient, db: Session):
+        """回归：同期间同 KPI 有多条 active 预算计划时，只应生成 1 条 open 告警
+
+        根因：database.py sessionmaker(autoflush=False)，端点内循环的 existing_alert
+        去重查询查不到本次刚 add 未 flush 的行 → 第二个计划重复 INSERT。
+        """
+        create_test_user(db)
+        token = get_token_for_user(client)
+        kpi = create_test_kpi(db, kpi_code="BUDGET_ALERT_DUP")
+        for _ in range(2):  # 两条同 KPI 计划（模拟数据面重复计划）
+            db.add(BudgetPlan(kpi_id=kpi.id, period="2026-06", budget_value=100.0,
+                              budget_year=2026, budget_month=6, status="active"))
+        from app.models import KPIValue
+        db.add(KPIValue(kpi_id=kpi.id, period="2026-06", actual_value=150.0))  # +50%
+        db.commit()
+
+        resp = client.post(f"{self.BASE}/deviation-check", headers=auth_header(token),
+                           json={"period": "2026-06", "threshold": 20})
+        assert resp.status_code == 200
+        assert resp.json()["alerts_generated"] == 1
+        from app.models import BudgetDeviationAlert
+        n = db.query(BudgetDeviationAlert).filter(
+            BudgetDeviationAlert.kpi_id == kpi.id,
+            BudgetDeviationAlert.period == "2026-06",
+            BudgetDeviationAlert.status == "open",
+        ).count()
+        assert n == 1, f"同 KPI 重复告警未去重，落库 {n} 条"
+
 
 class TestBudgetDeviationAlerts:
     """偏差预警记录查询/更新"""