在VBA中调试成功，稍作修改可以用于复杂网络的分级显示，呵呵

Dim WithEvents pp As Map
Dim tt As IMap
Dim str As String
Dim pFLDef As IFeatureLayerDefinition

Private Sub pp_ViewRefreshed(ByVal view As esriCarto.IActiveView, ByVal phase As esriCarto.esriViewDrawPhase, ByVal data As Variant, ByVal envelope As esriGeometry.IEnvelope)
    str = """等级路面-ID"" >" & Int(tt.MapScale / 800)
    pFLDef.DefinitionExpression = str
    Debug.Print "View: "; str
End Sub

Sub main()
    Dim md As IMxDocument
    Set md = ThisDocument
    Set pp = md.FocusMap
    Set tt = pp
    Dim pFLayer As IFeatureLayer
    Set pFLayer = tt.Layer(2)
    ' Set the definition query of the layer
    Set pFLDef = pFLayer
    ' QI from the FeatureLayer
    ' set the definition expression  pMxDoc.ActiveView.Refresh
End Sub