jquery ajax中文乱码


    <script type="text/javascript" src="/admin/js/jquery.js"></script>
    <script type="text/javascript">
    function test(){
        var s="靠";
        $.ajax({
        url: '/admin/WebService1.asmx/Test',
        type: 'POST',
        contentType :"application/x-www-form-urlencoded;charset=gb2312", 
        dataType:"xml",
        data:{s:s},
        success: function(msg){
            alert(msg.text);
        },
        error: function(x, e) {
            alert(x.responseText);
        }});
    }
    </script>
        [WebMethod]
        public string Test(string s)
        {
            throw new Exception();
        }这样的值会乱码，但是把contentType :"application/x-www-form-urlencoded;charset=gb2312",改成utf-8就不乱了，怎么才能让他用gb2312也不乱？随便问问