在StackOverflow得到最终原因及解决办法

http://stackoverflow.com/questions/16424117/php-unable-to-load-php-curl-dll-extension

libeay32.dll and ssleay32.dll have to be path-accessible for php_curl.dll loading to succeed. Copying them into System32 (or even into the Windows main directory) is a bad hack and does not even work with newer PHP versions.

The right way to do it is to add the PHP path to the Windows Path variable. In Control Panel -> System click on Advanced System Settings and use the button Environment Variables. UnderSystem Variables you will find the Path variable. Edit it and append ;C:\PHP to it - or whatever the path to your PHP folder is. Then restart Apache.

就是在环境变量里面添加PHP的路径。