<script src="jquery/jquery-1.3.2.min.js" type="text/javascript"></script>
<script src="jquery/jquery.form.js" type="text/javascript"></script>
<script type="text/javascript">
$(function(){
  $("#submit").bind("click",function(){
   $.ajax({
     type:"POST",
     url:"register.aspx",
     data:"UserName="+$("#username").val()+"&PassWord="+$("#pwd").val()+"Mail="+$("#mail").val(),
     success:function(msg){
     //alert(msg);
     }
   })
  })
})
</script>

   protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {
            Response.Write(Request.Form["username"]);//写不出来
        }
       
       
    }