string passName=FileUpload1.PostedFile.FileName.ToString();
int a=passName.LastIndexOf(".");
string expend_name=passName.Substring(a);//扩展名
string fileName = DateTime.Now.Millisecond.ToString() + FileUpload1.PostedFile.ContentLength.ToString()+ expend_name;//名字不对
FileUpload1.PostedFile.SaveAs(Server.MapPath("~//pic//") + fileName);