the RadGrid rendered in a wrong way.
I know my css, I used it before and there was nothing on it wrong. the only different is that I used VS2013 instead of VS2012,
So I searched about this problem.
and here is my search result.
there is some tag can be placed inside the web.config file
-- add this to the web.config file. <add key="vs:EnableBrowserLink" value="false" />this will fix the problem.
and here is a complete article about it.
The new Browser Link feature in VS 2013 is causing an error when DetailTable of Hierarchy RadGrid is expanded.
it looks like VS2013 problem, hope Microsoft solve it sooner.