diff --git a/app/models/course_member.rb b/app/models/course_member.rb
index d67994ef..788f87aa 100644
--- a/app/models/course_member.rb
+++ b/app/models/course_member.rb
@@ -15,6 +15,7 @@ class CourseMember < ActiveRecord::Base
       homeworks = course.homework_commons.includes(:homework_detail_manual).where("homework_type in (1, 3, 4)")
       if homeworks.count != 0
         homeworks.each do |hw|
+          next if hw.student_works.where(user_id: user_id).any?
           str += "," if str != ""
           str += "('#{hw.name}的作品提交',#{hw.id},#{user_id}, '#{Time.now.strftime('%Y-%m-%d %H:%M:%S')}', '#{Time.now.strftime('%Y-%m-%d %H:%M:%S')}')"
         end
@@ -34,6 +35,7 @@ class CourseMember < ActiveRecord::Base
       exercises = course.exercises
       if exercises.count != 0
         exercises.each do |ex|
+          next if ex.exercise_users.where(user_id: user_id).any?
           str += "," if str != ""
           str += "(#{ex.id},#{user_id}, 0, '#{Time.now.strftime('%Y-%m-%d %H:%M:%S')}', '#{Time.now.strftime('%Y-%m-%d %H:%M:%S')}')"
         end
@@ -53,6 +55,7 @@ class CourseMember < ActiveRecord::Base
       polls = course.polls
       if polls.count != 0
         polls.each do |poll|
+          next if poll.poll_users.where(user_id: user_id).any?
           str += "," if str != ""
           str += "(#{poll.id},#{user_id}, 0, '#{Time.now.strftime('%Y-%m-%d %H:%M:%S')}', '#{Time.now.strftime('%Y-%m-%d %H:%M:%S')}')"
         end
@@ -72,6 +75,7 @@ class CourseMember < ActiveRecord::Base
       tasks = course.graduation_tasks
       if tasks.count != 0
         tasks.each do |task|
+          next if task.graduation_works.where(user_id: user_id).any?
           str += "," if str != ""
           str += "(#{task.id}, #{user_id}, #{course.id}, '#{Time.now.strftime('%Y-%m-%d %H:%M:%S')}', '#{Time.now.strftime('%Y-%m-%d %H:%M:%S')}')"
         end