只能有一个啊,好象是把窗体的childform属性设置为true后,然后再判断吧。
Private Sub MDIForm_QueryUnload(Cancel As Integer, UnloadMode As Integer)
Dim frm As Form
For Each frm In Forms
If Not TypeOf frm Is MDIForm Then
MsgBox "有子窗体,名为" & frm.Name
Cancel = True
Exit Sub
End If
Next
End Sub