diff --git a/app/models/student_work.rb b/app/models/student_work.rb
index 384a75da1..a4ae63f04 100644
--- a/app/models/student_work.rb
+++ b/app/models/student_work.rb
@@ -111,7 +111,7 @@ class StudentWork < ApplicationRecord
 
   # 作品总体评价
   def overall_appraisal
-    return nil if work_status == 0
+    return "--" if work_status == 0
     case (self.work_score.to_f / homework_common.total_score).round(2)
     when (0.90..1.00)
       '优秀'