The problem has been solved , if someone has problem like this, please search csrf of yii and session of flash.
this will help you fix this problem
I use Uploadify(use Flash to upload file) on yii2, it display a HTTP 400 ERROR when i uploading file.
But if I use a Normal PHP script instead of Yii‘s Controller action to handel the flash request, it works.
Can someone tell me how to fix it or some tips? Thanks!