diff --git a/app/models/course.rb b/app/models/course.rb
index 45830c719..04b0535bd 100644
--- a/app/models/course.rb
+++ b/app/models/course.rb
@@ -35,7 +35,7 @@ class Course < ActiveRecord::Base
                      :delete_permission => :manage_files
 
   validates_presence_of :password, :term,:name
-  validates_format_of  :class_period, :with =>/^[1-9]\d*$/
+  validates_format_of  :class_period, :with =>/^\d*$/
   #validates_format_of  :name,:with =>/^[a-zA-Z0-9_\u4e00-\u9fa5]+$/
 
   before_save :self_validate
diff --git a/lib/legacy.rb b/lib/legacy.rb
new file mode 100644
index 000000000..5eeceabbc
--- /dev/null
+++ b/lib/legacy.rb
@@ -0,0 +1,26 @@
+class Legacy
+  def self.clear_period
+    begin
+      count = 0
+      puts '---------------------'
+
+      Course.transaction do
+        Course.all.each do |course|
+          if course.class_period =~ /^\D*$/
+            count += 1
+            puts "[#{course.id}]: #{course.name}"
+            puts "period #{course.class_period} ===> 0"
+            puts '---------------------'
+            course.class_period = '0' 
+            course.save
+          end
+        end # each end
+      end # transaction end
+
+      puts "clean period count: #{count}"
+    rescue Exception => ex
+      puts "*** transaction abored!"
+      puts "*** errors: #{ex.message}"
+    end
+  end
+end
diff --git a/lib/tasks/modify_courses_attr_type.rake b/lib/tasks/modify_courses_attr_type.rake
new file mode 100644
index 000000000..052c7f772
--- /dev/null
+++ b/lib/tasks/modify_courses_attr_type.rake
@@ -0,0 +1,8 @@
+desc "migrate old data."
+
+namespace :legacy do
+  desc "migrate Course class period data"
+  task :clear_period => :environment do
+    Legacy.clear_period
+  end
+end