ajax post跨域请求参数丢失

Question

使用jquery +ajax 发起post 请求需要跨域。在为ajax 添加跨域后发现post 请求参数丢失.

var ajaxRequest= $.ajax({
            url: subUrl+"/form/StuInformation" ,
            type:"POST",
            data:{
                "username": $.trim($("#subUsername").val()),
                "stuNickname": $.trim($("#subNickname").val()),
                "stuMajor": $.trim($("#subMajor").val()),
                "stuClass": $.trim($("#subClass").val()),
                "stuNo": $.trim($("#subNO").val()),
                "email": $.trim($("#subEmail").val()),
                "verificationCode": $.trim($("#checking").val()),
                "vaptcha_server": $.trim($("input[name='vaptcha_server']").val()),
                "vaptcha_token": $.trim($("input[name='vaptcha_token']").val())
            },
            dataType: "json",
            timeout: 3000,
            xhrFields: {
                withCredentials: true
            },
            crossDomain: true,
            success:function (data){
                if(data.statusCode==200){
                    //跳转到下载须知;
                }else{
                    alert(data.message);
                }
            },

            complete : function(XMLHttpRequest,status){ //请求完成后最终执行参数
                  if(status=='timeout'){//超时,status还有success,error等值的情况
                      ajaxRequest.abort();
                      alert("服务器超时")
                  }
            }

有哪位大神知道原因吗？帮忙解答一下吧