diff --git a/exam_pkg/api.py b/exam_pkg/api.py
index ba6e573..9296544 100644
--- a/exam_pkg/api.py
+++ b/exam_pkg/api.py
@@ -356,6 +356,8 @@ def api_grade_answers():
         answers = data.get('answers', [])
         if not answers:
             return error_response("MISSING_PARAMS", BAD_REQUEST, "缺少答案数据", http_status=400)
+        if not isinstance(answers, list):
+            return error_response("INVALID_PARAMS", BAD_REQUEST, "answers 必须为数组", http_status=400)
 
         # 校验每道题的 question_type
         for i, ans in enumerate(answers):