过去进行时是表示过去某一时刻或某一时间内正在进行或发生的动作。可以从两个方面来理解：1 过去某一时刻正在进行或发生的动作。E．g． They were playing football at ten o’clock yesterday morning． My mother was cooking when I got home． I was washing my clothes at this time yesterday． 2 过去某阶段持续进行的动作 What were you doing during the holiday? 另外，在复合句中，若主要动作和背景动作是同时发生的，那么主从句都可用过去进行时e．g． Jenny was reading while Danny was writing．
其结构是助动词be的过去形式was/were ＋v－ing．
其句式变化仍然要在be上做文章。E．g． We were working in class．
We weren’t working in class． Were you working in class?
过去进行时常与过去某一特定时间的状语连用，如 last night， at that time， at noon yesterday， last Sunday 等。 也有时没有时间状语，要通过上下文的暗示来确定用过去进行时。E．g． The students all worked hard． Everyone knew what he was working for．
做题时常见错误如下：
一、易把be＋现在分词记成be＋过去分词
例：He was talked （talk） to his mum at that time．
答案：was talking
解析：过去进行时与现在进行时结构上的区别体现在be动词上。
二、丢掉be动词或忘记把动词变成现在分词
例：1 I watching （watch） TV when he came in．
2 They were play （play） games at 5：00 p．m． yesterday．
答案：1 was watching 2 were playing
解析：现在进行时中“be＋现在分词，缺一不可”的规律也可应用于过去进行时。
三、对动词或动词词组提问时丢掉doing
例：We were flying kites at 5：00 p．m． yesterday． （对划线部分提问）
What were you at 5：00 p．m． yesterday?
答案：What were you doing at 5：00 p．m． yesterday?
解析：现在进行时中“What……doing……”?句式同样适用于过去进行时。