过去完成进行时表示过去某一时间之前一直进行的动作。
过去完成进行时表示动作在过去某一时间之前开始，一直延续到这一过去时间。和过去完成时一样，过去完成进行时也必须以一过去时间为前提。例如:
1.I had been looking for it for days before I found it.
这东西我找了好多天才找着的。
2.They had only been waiting for the bus a few minutes when it came.
他们只等了一会儿车就来了。
3.We had been studying this project for days before it put into effect.
这个项目我们研究了好几天才实施的。
4.We had only been waiting for the professor a few minutes when he arrived school.
我们只等了一会儿，教授就来学校了。
5.I had only been waiting for taxi a few minutes when it came.
我只等了一会儿，出租车就来了。
6.Our team had been practicing many times before we finished.
我们的团队练习了很多次才完成的。
7.The telephone had been ringing for three minutes before it was answered.
电话响了三分钟才接起来。
我们再来看看下面两个例句的区别：
1. Who's been eating my apples？
2. Who's eaten my apples？
第一句用过去完成进行时时态表示有强烈的感情色彩，表示愤怒不满，而第二句句只是希望回答的一个问题，并没有强烈的感情色彩。再有就是，第一句兼有进行时态，所以它表示的是所有苹果未被全部吃光的意思，而第二句是完成时态，说明苹果一个不剩了。