$.ajax({
                    type: "POST",
                    url: "ValueChange.ashx",
                    data: { sm: logInfo },
                    contentType: "application/text; charset=utf-8",
                    success: function() {
                        var session = '<%=Session["aa"]%>';
                        alert(session);
                        return true;
                    }
                });

using System;
using System.Collections;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Services;
using System.Web.Services.Protocols;
using System.Xml.Linq;
using System.Web.SessionState;

namespace ValueChangePro
{
    /// <summary>
    /// $codebehindclassname$ 的摘要说明
    /// </summary>
    [WebService(Namespace = "http://tempuri.org/")]
    [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
    public class Handler1 : IHttpHandler, IRequiresSessionState
    {

        public void ProcessRequest(HttpContext context)
        {
            context.Response.ContentType = "text/plain";
            var log = context.Request.QueryString["sm"];
            context.Session["aa"] = log;
        }

        public bool IsReusable
        {
            get
            {
                return false;
            }
        }
    }
}