1、表示原因。例句：
I didn’t hear what you said;I was looking at the picture.
我没有听见你的话，我在看那幅画。
I haven’t finished my homework yet,I was helping my mother in the kitchen all day yesterday.
我还没完成作业，我昨天一整天都在帮妈妈干厨房活。

2、对所说的话进行强调。在小说的对话中，有时引述动词不用一般过去时，而用过去进行时，意在强调所说的话，语气较重，且更为生动。例句：
A：“Did they catch her?”Mary was asking.
“他们抓住她了吗？”只听得玛丽问道。
B:”No,she escaped.”Tom told her.
“没有，她逃走了。”汤姆告诉她。

3、过去进行时还可和when结构遥相呼应，含有意外之意。例句：
I was walking in the street when someone called me.
我正在街上走时突然有人喊我。

4、表示与现在事实相反或将来的猜想情况，有时表示不耐烦等情绪。例句：
I was going to phone you,but I just didn’t have time.
我本想给你打电话的，但就是没有时间。
The basketball match was taking place the next day,but it had to be canceled because of the heavy rain.
篮球赛原定第二天举行的，但因大雨不得不取消。
I thought you were never coming.
我以为你总不会来了。

5、用来陈述原因或用作借口。
She went to the doctor yesterday. She was having a lot of trouble with her heart.
她昨天去看病了。她患了很严重的心脏病。

6、与always,constantly等词连用，表示感情色彩。例句:
The girl was always changing her mind.
这女孩老是改变主意。

7、表示动作的未完成性。过去进行时可以表示动作的未完成性，即对某事了解的不全面，希望得到更详细的情况。例句：
I was hearing Susan had entered the college.
我听说苏珊上了大学。

8、表示继续刚刚中断的谈话，用于日常生活中。例句：
As I were telling you,the boy took his stubbornness from his father.
正想我刚刚告诉你的，这孩子的犟脾气是他爸爸遗传给他的。
As she was telling me,we must depend upon ourselves to make our own way as best we can.
正如她所告诉我的，我们必须依靠自己竭尽全力走自己的路。

9、表示婉转语气，只限于want,hope,wonder等动词，用以提出请求。例句：
I was wondering if you could help me.
我想知道你是否能够帮助我。
I was hoping you could send me the book.
我想知道你是否能把书借给我。

10、表示对比。
例句： He was not sitting idle,he was making preparations.
他没有闲坐着，他在做准备。
While the children were playing in the shade,their parents were working in the scorching sun.
孩子们在树荫下玩耍，而他们的父母却在烈日下劳作。