Use standard methods and properties (FieldName, DataSet and ect.) of table component.
procedure TForm1.Button1Click(Sender: TObject); var Field: TField; i: Integer; begin Table1.Active:=False; for i:=0 to Table1.FieldDefs.Count-1 do Field:=Table1.FieldDefs[i].CreateField(Table1); Field:=TStringField.Create(Table1); with Field do begin FieldName:='New Field'; Calculated:=True; DataSet:=Table1; end; Table1.Active:=True; end;