在主窗体的“采购订单号”的获得焦点事件里面
Private Sub 采购订单号_GotFocus()
    On Error GoTo Err_采购订单号_GotFocus:
    Me.Parent.Form.cgddid = Me.采购订单号   '这一行要加，让父窗体的cgddid文本框获值 (要在主窗体里面加个文本框控件，名称写为cgddid)

    selectstr = Me.采购订单号
    Forms!usysfrmMain!labFind.Tag = 1
    Forms!usysfrmMain!btnEdit.Tag = 999
Exit_采购订单号_GotFocus:
    Exit Sub
Err_采购订单号_GotFocus:
    Resume Exit_采购订单号_GotFocus
End Sub