過去將來完成進行時用於表示從過去某一時間開始，一直延續到對過去來說的將來某一時間的動作。這種時態通常用於間接引語中，或者當我們需要表達過去某個時間點之後，某個動作或狀態會持續到另一箇過去的時間點時。
過去將來完成進行時的構成是“would have been + 現在分詞”。例如：
“He said that by the end of the spring term he would have been studying English for three years.” 表示到了春季學期末，他就學了三年英語了。
“I knew by that time he would have been working there for 30 years.” 表示到那時，他已經在那兒工作滿30年了。
“She told me she’d have been teaching in that university for 20 years by that summer.” 表示到那年夏天，她在那所大學教書就滿20年了。
在間接引語中，如果主句是過去時態，那麼用於賓語從句中的間接引語需要將將來完成進行時改爲過去將來完成進行時。例如：
“I know by this time next week you’ll have been working here for 30 years.” 變爲間接引語爲“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.” 變爲間接引語爲“She told me she’d have been teaching in that university for 20 years by that summer.”
此外，過去將來完成進行時也可以使用“should/would have been + v-ing”的形式，否定形式爲“should/would + not have been + v-ing”，疑問形式是將“should/would”提前。