diff --git a/app/models/homework_common.rb b/app/models/homework_common.rb
index c0882ec6f..6512c3f1d 100644
--- a/app/models/homework_common.rb
+++ b/app/models/homework_common.rb
@@ -170,7 +170,7 @@ class HomeworkCommon < ApplicationRecord
   #删除时更新题库中的引用数
   def update_homework_bank_quotes
     old_bank = self.homework_bank
-    old_bank.update_attributes(quotes: (old_bank.quotes - 1) > 0 ? (old_bank.quotes - 1) : 0, homework_common_id: nil)
+    old_bank.update_attributes(quotes: (old_bank.quotes - 1) > 0 ? (old_bank.quotes - 1) : 0, homework_common_id: nil) if old_bank.present?
   end
 
   # 查重是否有新结果