DateTime dtone = Convert.ToDateTime("2007-1-1 05:00:00");

DateTime dtwo = Convert.ToDateTime("2007-1-5 08:00:00");

TimeSpan span = dtwo .Subtract(dtone); //算法是dtwo减去 dtone 

string str  = span.Days + "天"  +span.Hours + "小时" + span.Minutes + "分钟" + + span.Seconds+"秒";