diff --git a/lib/qiniu/auth.rb b/lib/qiniu/auth.rb
index 7df31b6..cf379f3 100755
--- a/lib/qiniu/auth.rb
+++ b/lib/qiniu/auth.rb
@@ -51,15 +51,13 @@ module Qiniu
           :callback_body          => "callbackBody"        ,
           :persistent_ops         => "persistentOps"       ,
           :persistent_notify_url  => "persistentNotifyUrl" ,
-          :transform              => "transform"           ,
 
           # 数值类型参数
           :deadline               => "deadline"            ,
           :insert_only            => "insertOnly"          ,
           :fsize_limit            => "fsizeLimit"          ,
           :detect_mime            => "detectMime"          ,
-          :mime_limit             => "mimeLimit"           ,
-          :fop_timeout            => "fopTimeout"
+          :mime_limit             => "mimeLimit"
         } # PARAMS
 
         public
@@ -140,16 +138,29 @@ module Qiniu
           access_key = Config.settings[:access_key]
           secret_key = Config.settings[:secret_key]
 
+          download_url = url
+
+          ### URL变换：追加FOP指令
+          if args[:fop].is_a?(String) && args[:fop] != '' then
+            if download_url.index('?').is_a?(Fixnum) then
+              # 已有参数
+              download_url = "#{download_url}&#{args[:fop]}"
+            else
+              # 尚无参数
+              download_url = "#{download_url}?#{args[:fop]}"
+            end
+          end
+
           ### 授权期计算
           e = Auth.calculate_deadline(args[:expires_in], args[:deadline])
 
           ### URL变换：追加授权期参数
-          if url.index('?').is_a?(Fixnum) then
+          if download_url.index('?').is_a?(Fixnum) then
             # 已有参数
-            download_url = "#{url}&e=#{e}"
+            download_url = "#{download_url}&e=#{e}"
           else
             # 尚无参数
-            download_url = "#{url}?e=#{e}"
+            download_url = "#{download_url}?e=#{e}"
           end
 
           ### 生成数字签名
diff --git a/spec/qiniu/auth_spec.rb b/spec/qiniu/auth_spec.rb
index afb54bc..c8a7a81 100755
--- a/spec/qiniu/auth_spec.rb
+++ b/spec/qiniu/auth_spec.rb
@@ -1,4 +1,5 @@
 # -*- encoding: utf-8 -*-
+# vim: sw=2 ts=2
 
 require 'spec_helper'
 require 'qiniu/auth'
@@ -56,7 +57,12 @@ module Qiniu
           result.body.should_not be_empty
 
           ### 授权下载地址（带参数）
-          download_url = Qiniu::Auth.authorize_download_url(url + '?download/a.m3u8')
+          download_url = Qiniu::Auth.authorize_download_url(
+            url,
+            {
+              :fop => 'download/a.m3u8'
+            }
+          )
           puts "download_url=#{download_url}"
 
           result = RestClient.get(download_url)