>Thank you very much for your reply. But the problem is , I only want to solve the problem on datatable not on sql server.
>For example, in visual fox, it allow us to use sql expression but datatable in vb.net is not.

Then you could use Linq to DS. eg.:

Dim list = ds.Tables("tb_ItemList").AsEnumerable()
Dim sublist = ds.Tables("SubList").AsEnumerable()

'Option 1
Dim result = From l In list Join sl In sublist On l.Field(Of Integer)("ItemCode") = sl.Field(Of Integer)("ItemCode") _
 Into tmp From tmp2 In tmp.DefaultIfEmpty() _
 Where tmp2 Is Nothingl

'Option 2
Dim subCodes = sublist.[Select](Function(x) x.Field(Of Integer)("ItemCode"))
Dim result2 = From r In list Where Not subCodes.Contains(r.Field(Of Integer)("ItemCode"))r

Disclaimer: auto converted from C# and not tested.....