protected void Page_Load(object sender, EventArgs e)
    {
        Ajax.Utility.RegisterTypeForAjax(typeof(Test_TestAjaxnet));
    }

   [Ajax.AjaxMethod(HttpSessionStateRequirement.ReadWrite)]
    public Object GetValue(string newparam)
    {
        Session.Add("tt", "gg");
        return new string[2] { newparam, this.GetTest() };
    }

    JS:
        function onchangeText()
        {
            var getvalue = Test_TestAjaxnet.GetValue('newparam');
            var txt = document.getElementById("Text1");
            txt.value = getvalue.value[0] + getvalue.value[1];
        }

------解决方案--------------------
通过js端直接传参数调用服务端方法，在服务端方法进行业务处理