您好，我测试了您的代码缺失存在问题，感谢反馈! 另外我测试了另外一种方法请试用：

    <CommandMethod("test2", CommandFlags.Modal)>
    Public Sub Test2()
        Dim ed As Editor = Application.DocumentManager.MdiActiveDocument.Editor
        Try
            Dim opt As New OpenFileDialog("请选择文件", "", "dwg", "", OpenFileDialog.OpenFileDialogFlags.DoNotTransferRemoteFiles)
            Dim re As System.Windows.Forms.DialogResult
            re = opt.ShowDialog()
            If re = System.Windows.Forms.DialogResult.OK Then
                ed.WriteMessage(opt.Filename)
            End If
        Catch ex As Exception
        End Try
    End Sub