我始终搞不懂过去式和过去完成式的分别

比较过去时与现在完成时

1）过去时表示过去某时发生的动作或单纯叙述过去的事情，强调动作；现在完成时为过去发生的，强调过去的事情对现在的影响，强调的是影响。

2）过去时常与具体的时间状语连用，而现在完成时通常与模糊的时间状语连用，或无时间状语。

一般过去时的时间状语:
yesterday, last week，…ago, in1980, in October, just now, 具体的时间状语

共同的时间状语:
this morning, tonight,this April, now, once，before, already, recently，lately

现在完成时的时间状语
for, since, so far, ever, never, just, yet, till / until, up to now, in past years, always,
不确定的时间状语

3）现在完成时可表示持续到现在的动作或状态，动词一般是延续性的，如live, teach, learn, work, study, know.
过去时常用的非持续性动词有come, go, leave, start, die, finish, become, get married等。
举例：
I saw this film yesterday.
（强调看的动作发生过了。）
I have seen this film.
（强调对现在的影响，电影的内容已经知道了。）
Why did you get up so early?
（强调起床的动作已发生过了。）
Who hasn't handed in his paper?
（强调有卷子，可能为不公平竞争。）
She has returned from Paris.
她已从巴黎回来了。
She returned yesterday.
她是昨天回来了。
He has been in the League for three years.
(在团内的状态可延续)
He has been a League member for three years.
(是团员的状态可持续)
He joined the League three years ago.
( 三年前入团，joined为短暂行为。)
I have finished my homework now.

---Will somebody go and get Dr. White?
---He's already been sent for.
句子中如有过去时的时间副词（如 yesterday, last, week, in 1960）时，不能使用现在完成时，要用过去时。
（错）Tom has written a letter to his parents last night.
（对）Tom wrote a letter to his parents last night.

过去完成时

1） 概念：表示过去的过去
----|-------|-----|---->其构成是had +过去分词构成。
那时以前 那时 现在

2） 用法
a. 在told, said, knew, heard, thought等动词后的宾语从句。
She said (that) she had never been to Paris.
b. 状语从句
在过去不同时间发生的两个动作中，发生在先，用过去完成时；发生在后，用一般过去时。
When the police arrived, the thieves had run away.
c. 表示意向的动词，如hope, wish, expect, think, intend, mean, suppose等，用过去完成时表示"原本…，未能…"
We had hoped that you would come, but you didn't.

3) 过去完成时的时间状语before, by, until , when, after, once, as soon as。
He said that he had learned some English before.
By the time he was twelve, Edison had began to make a living by himself.
Tom was disappointed that most of the guests had left when he arrived at the party.

典型例题
The students ___ busily when Miss Brown went to get a book she ___ in the office.
A. had written, left B，were writing, has left C. had written, had left D. were writing, had left
答案D. "把书忘在办公室"发生在"去取书"这一过去的动作之前，因此"忘了书"这一动作发生在过去的过去，用过去完成时。句中when表示的是时间的一点，表示在"同学们正忙于……"这一背景下，when所引导的动作发生。因此
前一句应用过去进行时。

注意： had no … when 还没等…… 就……
had no sooner… than 刚…… 就……
He had no sooner bought the car than he sold it.

如果还有不懂或不明白的地方，欢迎继续提问？

过去式是用来表达动词的“过了”、“完了”，“结束了”等意思，和现在的状态没有关系。
一般过去式 表示过去的动作和状态。 I met him yesterday. 昨天我碰见了他。

过去完成时表示在过去某一时间或动作之前已经发生或完成了的动作。
它表示句子中描述的动作发生在“过去的过去”。
具体如下：
过去完成时的基本用法
（1）表示在过去某一时刻或动作以前完成了的动作，即“过去的过去”。可以用by,
before等介词短语或一个时间状语从句来表示，也可以用一个表示过去的动作来表示，还可能通过上下文来表示。例如：
By nine o’clock last night, we had got 200 pictures from the
spaceship.到昨晚9点钟，我们已经收到200 张飞船发来的图片。
（2）表示由过去的某一时刻开始，一直延续到过去另一时间的动作或状态，常和for, since构成的时间状语连用。例如：
I had been at the bus stop for 20 minutes when a bus finally
came.当车来的时候，我在车站已等了20分钟。
He said he had worked in that factory since 1949.他说自从1949年以来他就在那家工厂工作。
（3）叙述过去发生的事情，在已叙述了过去发生的事情后，反过来追述或补述以前发生的动作时，常使用过去完成时。例如：
Mr. Smith died yesterday. He had been a good friend of
mine.史密斯先生昨天去世了。他以前是我的好友。
I didn’t know a thing about the verbs, for I had not studied my
lesson.我对动词一无所知，因为我没有好好学习功课。
（4）在含有定语从句的主从复合句中，如果叙述的是过去的事，先发生的动作常用过去完成时。例如：
I returned the book that I had borrowed.我已归还了我借的书。
She found the key that she had lost.她丢失的钥匙找到了。
（5）过去完成时常常用在宾语从句（或间接引语）中，这时从句中的动作发生在主句表示的过去的动作之前。例如：
He said that he had known her well.他说他很熟悉她。
I thought I had sent the letter a week before. 我认为我一星期前就把信寄出去了。
（6）在包含有when,
until等连词的复合句中，如果主句谓语动词和从句谓语动词所表示的过去动作不是同时发生的，那么先发生的动作通常用过去完成时表示。例如：
When I woke up, it had already stopped raining.我醒来时雨已停了。
She didn’t go to bed until she had finished he work.她直到把工作做完之后才睡觉。
注意：如果两个动作紧接着发生，则常常不用过去完成时，特别是在包含before和after的复合句中，因为这时从句的动作和主句的动作发生的先后顺序已经非常明确，这时可以用一般过去时代替过去完成时。例如：
After he arrived in England, Marx worked hard to improve his
English.马克思到达英格兰之后，努力提高他的英语水平。
（7）动词think, want, hope, mean, plan,
intend等用过去完成时来表示过去未曾实现的想法，希望，打算或意图等。例如：
They had wanted to help but could not get there in
time.他们本来打算去帮忙，但没有及时赶到那里。
We had hoped to be able to come and see you .我们本来希望能来看看你。
（8）过去完成时还可用在hardly…when…, no sooner…than…, It was the first (second, etc)
time (that)…等固定句型中。例如：
Hardly had he began to speak when the audience interrupted
him.他刚开始演讲，听众就打断了他。
No sooner had he arrived than he went away again.他刚到就又走了。
It was the third time that he had been out of work that year.这是他那一年第三次失业了。

1. 一般过去时表示过去某个时间发生的事、存在的状态或经常发生的动作。说话的侧重点只在于陈述一件过去的事情，不强调对“现在”产生的影响。如：

He visited Guilin in 1998.他1998年参观过桂林。(只说明去桂林的时间)

2:过去完成

一、构成
过去完成时由“助动词had+过去分词”构成,had没有人称和数的变化,可以帮助构成疑问句和否定句。如:
He had lived in Shanghai for three years before he came here.
How many English words had you learned by the end of last week?
I had not gone much farther before I caught them up.
二、基本用法
过去完成时表示在过去某一时间或动作之前已经发生或完成了的动作。它表示动作发生的时间是“过去的过去”。因此,过去完成时是一个相对的时态,它不能离开过去时间而独立存在。如:
【正】I had finished my homework before supper.
【误】I had finished my homework.(没有任何时间可以作参照进行对比)
【正】They became good friends after they had talked heart to heart.
【误】They had become good friends after they talked heart to heart.(动作的先后与时态不符)

过去式是过去发生的事情.过去完成式是过去某一个时间点之前完成的事情,即过去的过去.
I read book yestaday.过去式,意思是:我昨天读书
I had read the book before yestoday.过去完成式,意思是:我昨天就读过书了

其实很简单的，描述过去的事情用过去时，过去的过去是过去完成时。