diff --git a/app/models/poll.rb b/app/models/poll.rb
index b0499b572..d2f5b40fe 100644
--- a/app/models/poll.rb
+++ b/app/models/poll.rb
@@ -44,7 +44,9 @@ class Poll < ActiveRecord::Base
   def act_as_course_activity
     if self.polls_type == "Course"
       if self.polls_status == 2 #问卷是发布状态
-        self.course_acts << CourseActivity.new(:user_id => self.user_id,:course_id => self.polls_group_id)
+        if CourseActivity.where(:course_id => self.polls_group_id, :user_id => self.user_id, :course_act_id => self.id, :course_act_type => 'Poll').count == 0
+          self.course_acts << CourseActivity.new(:user_id => self.user_id,:course_id => self.polls_group_id)
+        end
       elsif self.polls_status == 1 #问卷是新建状态
         self.course_acts.destroy_all
       end
diff --git a/db/migrate/20161216031906_delete_course_activities.rb b/db/migrate/20161216031906_delete_course_activities.rb
new file mode 100644
index 000000000..dbbe193ce
--- /dev/null
+++ b/db/migrate/20161216031906_delete_course_activities.rb
@@ -0,0 +1,14 @@
+class DeleteCourseActivities < ActiveRecord::Migration
+  def up
+    course_acts = CourseActivity.where(:course_id => 844, :user_id => 10096, :course_act_id => 436, :course_act_type => 'Poll')
+
+    if course_acts.count > 1
+      course_acts.limit(course_acts.count - 1).each do |act|
+        act.delete
+      end
+    end
+  end
+
+  def down
+  end
+end