foreach (DataRow dr1 in dt1.Rows)
{
    foreach (DataRow dr2 in dt2.Rows)
    {
         if (dr1["id"].ToString() == dr2["id"].ToString())
         {
              dr1.Delete();
              dr2.Delete();
              break;
          }
     }
 }

dt.AcceptChanges();//

 DataTable dt1 = new DataTable();
 DataTable dt2 = new DataTable(); 
var dt3 = from r in dt1.AsEnumerable() where
 !( from rr in dt2.AsEnumerable() select rr.Field<int>("Id") ).Contains(
   r.Field<int>("Id")) select r;

------解决方案--------------------
探讨

dt2.AsEnumerable().Except(dt1.AsEnumerable())