它一直在我的鼻子底下，在managementObject上使用GetPropertyValue("AccessMask")获得权限级别。

完整方法：

Dim l_managemantObject As ManagementBaseObject() = CType(securityDescriptor.Properties("DACL").Value, ManagementBaseObject())

    For Each mObject As ManagementBaseObject In l_managemantObject
        l_name = CType(mObject.GetPropertyValue("Trustee"), ManagementBaseObject).Properties("Name").Value.ToString
        If CType(mObject.GetPropertyValue("Trustee"), ManagementBaseObject).Properties("Domain").Value IsNot Nothing Then
           l_domain = CType(mObject.GetPropertyValue("Trustee"), ManagementBaseObject).Properties("Domain").Value.ToString()
        End If

        Dim l_accessMask as UInteger = mObject.GetPropertyValue("AccessMask")

        If users.UserName.ToLower = (l_domain & "\" & l_name).ToLower Then
           if l_accessMask = 2032127 then
              Return True  
           endif                             
        End If
    Next