将来完成时用来表示在将来某一时间以前已经完成或一直持续的动作。经常与before+将来时间或by+将来时间连用，也可与before或by the time引导的现在时的从句连用。
一、结构形式
过去完成进行时由“will / shall have been+现在分词”构成，通常还会有其他状语成分表示时间长短。
二、用法归纳
用法一：表示动作从某一时间开始一直延续到将来某一时间，至于是否继续下去，要视上下文而定。如：
She will have been having treatment all her life.
她将终生受到治疗。
By the end of next month he will have been here for ten years.
到下月底，他在这儿就够十年了。
By this time next year, we will have been doing business with each other for 20 years.
到明年这时候，我们的业务住来就满20年了。
By the end of this year he’ll have been acting for thirty years.
到今年年底他当演员就满30年了。
用法二：表示一种经常性反复进行的持续性动作。如：
By the end of this month he will have been training horses for twenty years.
到了这个月底他驯马就满20年了。
By the end of this month he will have been climbing mountains for twenty years.
到了这个月底他登山就满20年了。
Before turning into 42, Tom will have been jogging for 10 years.
在汤姆满42岁之前，他坚持慢跑10年了。
