1. 现在完成时：由“have/has + 过去分词”构成，表示过去某动作、状态等一直延续到现在或对现在有影响，如：
　　　　We have learned 500 new words this term.
　　　　John has lived in London for ten years.

　　2. 过去完成时：由“had + 过去分词”构成，表示过去某时前已经发生的动作或情况，如：
　　　　Peter didn't go to see the film because he had seen it twice.
　　　　He had done morning exercises before he had his breakfast.

　　3. 将来完成时：由“will have + 过去分词”构成，表示将来某时之前业已发生的事，常与时间状语“by + 时间”连用，如：
　　　　By the end of next month they will have completed the project.

　　4. 现在完成进行时：由“have/has been + 现在分词”构成，表示过去某动作一直延续到现在并且还在继续，或刚结束，如：
　　　　It has been snowing for several days.
　　　　The police have been trying to find an answer to the mystery of the man's death.