步骤：
0.html：

<input id="btn" type="button" value="ajax json" /> 
    <input id="btn2" type="button" value="ajax content" /> 

    <input id="txt4" type="text" value="456" />
    <input id="txt1" type="text" value="123" /> 
    <input id="txt2" type="text" value="234" /> 
    <input id="txt3" type="text" value="345" /> 

1.使用json数据形式

$(document).ready(function () {
        $("#btn").click(function () {
            
            $.ajax({
                type: 'POST',
                url: "/Student/MyAjax",
                data: {
                    val1: $("#txt1").val(),
                    val2: $("#txt2").val(),
                    val3: $("#txt3").val(),
                    val4: $("#txt4").val()
                },
                 success: function (obj) { alert(obj["stuNo"] + "," + obj["classId"] + "," + obj["name"]);},
                dataType: "json"
               
            });
            
        });
    });

[HttpPost]//记得要加HTTPPOST标记！
        public JsonResult MyAjax(FormCollection f)
        {
            string val1 = f["val1"].ToString();
            string val2 = f["val2"].ToString();
            string val3 = f["val3"].ToString();
            string val4 = f["val4"].ToString();
            Student s = new Student()
            {
                stuNo = val1,
                classId = val2,
                name = val3
            };


            return Json(s);
        }

2.直接传字符串：

$("#btn2").click(function () {
            $.ajax({
                type: 'POST',
                url: "/Student/MyAjax2",
                data: "val1=" + $("#txt1").val() + "&val2=" + $("#txt2").val() +
                 "&val3=" + $("#txt3").val() + "&val4=" + $("#txt4").val(),
                success: function (obj) { alert(obj); }
            });
        });

[HttpPost]
        public ContentResult MyAjax2(FormCollection f)
        {
            string val1 = f["val1"].ToString();
            string val2 = f["val2"].ToString();
            string val3 = f["val3"].ToString();
            string val4 = f["val4"].ToString();
            string s = "";
            s += val1 + ",";
            s += val2 + ",";
            s += val3 + ",";
            s += val4 ;

            return Content(s);
        }