GAE not support PHP cURL, so how should we implement Facebook SDK on our application?

I Assume you are using CodeIgnitor to develop your applications:

1. First, download PHP-SDK from this branch: https://github.com/camfitz/facebook-php-sdk

2. Follow this page: http://www.galalaly.me/index.php/2012/04/using-facebook-php-sdk-3-with-codeigniter-2-1/ to do the rest