System.Web.Script.Serialization.JavaScriptSerializer jss = new System.Web.Script.Serialization.JavaScriptSerializer(); 序列化

//将序列化成json格式后日期(毫秒数)转成日期格式
        function ChangeDateFormat(cellval) {
            var date = new Date(parseInt(cellval.replace("/Date(", "").replace(")/", ""), 10));
            var month = date.getMonth() + 1 < 10 ? "0" + (date.getMonth() + 1) : date.getMonth() + 1;
            var currentDate = date.getDate() < 10 ? "0" + date.getDate() : date.getDate();
            return date.getFullYear() + "-" + month + "-" + currentDate;
        }

调用：ChangeDateFormat(json[i].PTime)；

如果是Newtonsoft.Json　则

Newtonsoft.Json.Converters.IsoDateTimeConverter iso = new Newtonsoft.Json.Converters.IsoDateTimeConverter();
                iso.DateTimeFormat = "yyyy-MM-dd";
                string json = JsonConvert.SerializeObject(dt, Formatting.Indented, iso);

return JsonConvert.DeserializeObject<ApiResponse<T>>(strResult, new JsonSerializerSettings
            {
                ReferenceLoopHandling = ReferenceLoopHandling.Ignore
            });