How to use Request.Form["xxxx"] in ASP.NET web form application mode

HI,all have a question about Request.Form
I use VisualStudio2013 to create a new [ASP.NET web Form application] project. have one .aspx file need to use Request.Form["xxxx"] to get querystring data but it's not work,the get value is null
so I create another new project use [asp.net Empty web application] use same files to test the Request.Form["xxxx"] ,it's work!!
so I need to know how to fix this question thank you