if self.params[0].value:

     mxd = arcpy.mapping.MapDocument(self.params[0].value.value)

     dataFrames = arcpy.mapping.ListDataFrames(mxd)

     dfList = []

     for df in dataFrames:

       dfList.append(df.name)

       dfList.sort()

     if not self.params[1].altered:

       self.params[1].filter.list = dfList

参考 : https://blog.csdn.net/sprintwater/article/details/41146543