完成进行式不定词用来表达动词后一个持续性丶但现在已完成的动作。完成进行式不定词的构成为：
to have been 现在分词
如同现在式不定词，有些时候必须用上不带 to 的被动语态不定词，因此 to 会被省略掉。这种情况会发生在多数情态助动词后，以及用在其他使用零不定词的地方。
举例
- the woman seemed to have been crying.
- he pretended to have been painting all day.
- i would have preferred to have been sleeping all afternoon.
- you must have been waiting for hours!
- they might have been talking before you came in.
- you should have been studying for your test.