diff --git a/lib/upyun.rb b/lib/upyun.rb
index b900b9f..614cdeb 100644
--- a/lib/upyun.rb
+++ b/lib/upyun.rb
@@ -1,6 +1,7 @@
 require 'upyun/version'
 require 'upyun/utils'
 require 'upyun/rest'
+require 'upyun/form_base'
 require 'upyun/form'
 
 module Upyun
diff --git a/lib/upyun/form.rb b/lib/upyun/form.rb
index 4dc90e6..451bc63 100644
--- a/lib/upyun/form.rb
+++ b/lib/upyun/form.rb
@@ -1,60 +1,24 @@
 # encoding: utf-8
 require 'restclient'
-require 'base64'
 require 'json'
-require 'active_support/hash_with_indifferent_access'
 
 module Upyun
-  class Form
-    include Utils
+  class Form < FormBase
 
-    VALID_PARAMS = %w(
-      bucket
-      save-key
-      expiration
-      allow-file-type
-      content-length-range
-      content-md5
-      content-secret
-      content-type
-      image-width-range
-      image-height-range
-      notify-url
-      return-url
-      x-gmkerl-thumbnail
-      x-gmkerl-type
-      x-gmkerl-value
-      x-gmkerl-quality
-      x-gmkerl-unsharp
-      x-gmkerl-rotate
-      x-gmkerl-crop
-      x-gmkerl-exif-switch
-      ext-param
-    )
-
-    attr_accessor :bucket, :password
     attr_reader :options
 
     def initialize(password, bucket, options={timeout: 60})
-      @password = password
-      @bucket = bucket
+      super(api_secret: password, bucket: bucket)
       @options = options
       @endpoint = ED_AUTO
     end
 
     def upload(file, opts={})
-      base_opts = HashWithIndifferentAccess.new({
-        'bucket' => @bucket,
-        'save-key' => '/{year}/{mon}/{day}/{filename}{.suffix}',
-        'expiration' => Time.now.to_i + 600
-      })
-
       payload = {
-        policy: policy(base_opts.merge(opts)),
+        policy: policy(opts),
         signature: signature,
         file: file.is_a?(File) ? file : File.new(file, 'rb')
       }
-
       rest_client.post(payload, {'User-Agent' => "Upyun-Ruby-SDK-#{VERSION}"}) do |res|
         case res.code
         when 302
@@ -81,24 +45,8 @@ def upload(file, opts={})
       end
     end
 
-    private
-      def policy(opts)
-        @_policy = Base64.strict_encode64(policy_json(opts))
-      end
-
-      def signature
-        md5("#{@_policy}&#{@password}")
-      end
-
-      def policy_json(opts)
-        policies = VALID_PARAMS.reduce({}) do |memo, e|
-          (v = opts[e]) ? memo.merge!({e => v}) : memo
-        end
-        policies.to_json
-      end
-
-      def rest_client
-        @rest_clint ||= RestClient::Resource.new("http://#{@endpoint}/#{@bucket}", options)
-      end
+    def rest_client
+      @rest_clint ||= RestClient::Resource.new("http://#{@endpoint}/#{@bucket}", options)
+    end
   end
 end
diff --git a/lib/upyun/form_base.rb b/lib/upyun/form_base.rb
new file mode 100644
index 0000000..c867107
--- /dev/null
+++ b/lib/upyun/form_base.rb
@@ -0,0 +1,68 @@
+# encoding: utf-8
+require 'base64'
+require 'json'
+require 'active_support/hash_with_indifferent_access'
+
+module Upyun
+  class FormBase
+    include Utils
+
+    VALID_PARAMS = %w(
+      bucket
+      save-key
+      expiration
+      allow-file-type
+      content-length-range
+      content-md5
+      content-secret
+      content-type
+      image-width-range
+      image-height-range
+      notify-url
+      return-url
+      x-gmkerl-thumbnail
+      x-gmkerl-type
+      x-gmkerl-value
+      x-gmkerl-quality
+      x-gmkerl-unsharp
+      x-gmkerl-rotate
+      x-gmkerl-crop
+      x-gmkerl-exif-switch
+      ext-param
+    )
+
+    attr_accessor :api_secret, :bucket, :password, :params
+    alias_method :password, :api_secret
+
+    def initialize(api_secret:, bucket:, params: {})
+      @api_secret, @bucket, @params = api_secret, bucket, params
+    end
+
+    def policy(params={})
+      opts = default_params.merge params
+      @_policy = Base64.strict_encode64(policy_json opts)
+    end
+
+    def signature
+      md5("#{@_policy}&#{@api_secret}")
+    end
+
+    def policy_json(opts)
+      policies = VALID_PARAMS.reduce({}) do |memo, e|
+        (v = opts[e]) ? memo.merge!({e => v}) : memo
+      end
+      policies.to_json
+    end
+
+    ##
+    # 默认参数
+    def default_params
+      HashWithIndifferentAccess.new({
+        'bucket' => @bucket,
+        'save-key' => '/{year}/{mon}/{day}/{filename}{.suffix}',
+        'expiration' => Time.now.to_i + 600
+      }).merge @params
+    end
+
+  end
+end
\ No newline at end of file