检查块是否存在..

On Error Resume Next
Dim ss As AcadSelectionSet
Set ss = ThisDrawing.SelectionSets.Item("abcd")
If Err.Number  0 Then
    Set ss = ThisDrawing.SelectionSets.Add("abcd")
    Err.Clear
Else
    ss.Clear
End If

Dim Mycollection As AcadSelectionSets
Dim SSet1 As AcadSelectionSet
' first check if any ss exist and if they do, delete them
        Set Mycollection = ThisDrawing.SelectionSets
             For Each SSet1 In Mycollection
                 If SSet1.Name = "MySS" Then
                     ThisDrawing.SelectionSets.Item("MySS").Delete
                     Exit For
                 End If
             Next