以往完成进行时由“would have been 现在分词”组成。
He said that by the end of the spring term he would have been studying English for three years. 他说道来到春天期末，他学了三年英文了。
I want you thinking of food and wine, because these last years would have been miserable for you. 我想要你只为吃吃喝喝，由于最近几年你的日常生活够苦的。
I know by this time next week you’ll have been working here for 30 years.
→I knew by that time he would have been working there for 30 years.
She will have been teaching in this university for 20 years by this summer.
→She told me she’d have been teaching in that university for 20 years by that summer.
英语时态：情态动词 have 以往分词的用法