string currUrl = Request.Url.ToString();
if (currUrl == "http://第一种域名")
{
    //....
}
if (currUrl == "http://第二种域名")
{ 
    //....
}

------解决方案--------------------

首先lz要把问题说清楚:
1.如果是根据域名来显示不同的模块:
C# code

string currUrl = HttpContext.Current.Request.Url.Host;
if (currUrl =="域名1")
{
}
else
{
}