DateTime转换为timeStamp：  

            DateTime dt = DateTime.Now;

            DateTime startTime = TimeZone.CurrentTimeZone.ToLocalTime(new DateTime(1970, 1, 1));

            TimeSpan timeSpan = dt.Subtract(startTime);

            string timeStamp = timeSpan.Ticks.ToString();

            return timeStamp.Substring(0, timeStamp.Length - 7);

timeStamp转换为DateTime：

           string timeStamp = "1144821796";

            DateTime dtStart = TimeZone.CurrentTimeZone.ToLocalTime(new DateTime(1970,1,1));

            long lTime = long.Parse(timeStamp + "0000000");

            TimeSpan toNow = new TimeSpan(lTime);

            DateTime dtResult = dtStart.Add(toNow);