He thought，“She was watching me when I passed．”= He thought that she had been watching him when he had passed．

3.过去完成进行时经常与现在完成进行时混淆。
现在完成进行时 (The present perfect progressive) 由 have/has been +-ing 分词构成；
过去完成进行时（ The past perfect progressive tenses ）由 had been +-ing 分词构成．
现在/过去完成进行时的用法：
A. 在某段时间内一直进行的动作用现在完成进行时来强调动作在某段时间里的持续性．
动作通常有"现在"的结果，要根据上下文来确定到"现在"为止，动作是否还在继续进行．
同样，过去完成进行时表示在过去更早时间内进行的动作,并对过去某一时刻产生结果。
B.表示重复动作的现在/过去完成进行时
我们也可以用完成进行时形式来表示现在或过去经常重复的动作
注意：过去完成进行时和过去完成时类似，需要有过去这一时间点。

过去完成进行时与过去完成时比较：
过去完成进行时与过去完成时的用法很相近，它通常表示某个过去正在进行的动作或状态，持续到过去某个时刻，还未完成，一直持续到之后的当前才结束
He had been waiting for two weeks． He was still waiting．（有一个表示一段时间的状语）
Up to that time he had been translating those books．（He was still translating at “that time”．）
He had been writing the letter till two o'clock．
He was now thirty years old．He had been gambling since he was ten．（He was still gambling at thirty．）
He had been standing there in the sun．（没有时间状语）
He had been thinking about his marriage．
不过这种时态并不一定表示这个过去动作将持续下去：
He came back at seven．He had been waiting for her two hours．（At seven he did not wait any more．）
He stopped swimming．He had been swimming for the last three hours．

过去完成进行时用法：
①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。
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。
They had only been waiting for the bus a few moments when it came.
他们只等了一会儿车就来了。

②表示反复的动作。
He had been mentioning your name to me.
他过去多次向我提到过你的名字。
You had been giving me everything.
你对我真是有求必应。

③过去完成进行时还常用于间接引语中
The doctor asked what he had been eating
.医生问他吃了什么。
I asked where they had been staying all those days.
我问他们那些天是呆在哪儿的。

④过去完成进行时之后也可接具有“突然”之意的when分句。
I had only been reading a few minutes when he came in.
我刚看了几分钟他就进来了。
She'd only been reviewing her lessons for a short while when her little sister interrupted her.
她温习功课才一会儿，她妹妹就打断她了。
I had been sleeping when my friend telephone me.
我正在睡觉时，我的朋友给我打电话。