1：在你sdk安装的目录里面找 flex-sdk-description.xml
2：在FLEX的命令行里面输入mxmlc -version 回车
3：通过代码：
<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2008/10/29/determining-your-flex-sdk-version-number/ -->
<mx:Application name="mx_internal_VERSION_test"
xmlns:mx="http://www.adobe.com/2006/mxml"
layout="vertical"
verticalAlign="middle"
backgroundColor="white">
<mx:Label text="{mx_internal::VERSION}" />
</mx:Application>
<!-- http://blog.flexexamples.com/2008/10/29/determining-your-flex-sdk-version-number/ -->
<mx:Application name="mx_internal_VERSION_test"
xmlns:mx="http://www.adobe.com/2006/mxml"
layout="vertical"
verticalAlign="middle"
backgroundColor="white">
<mx:Label text="{mx_internal::VERSION}" />
</mx:Application>
来自：http://blog.flexexamples.com/2008/10/29/determining-your-flex-sdk-version-number/