when/while两者都表示“当...时候”.一般来说,在主从复合句中,当主语中的动作正在进行时,when连接的从句中的动作才发生,while连接的从句中正在进行时,主句的动作才发生.
1、when可以指动作一前一后发生（主从复合句中的动词都为瞬间动词），也可以指一个动作发生在另外一个动作之间（主从复合句的动词一个是瞬间动词一个是延续性动词）。
The train had left when I got to the station.
I met one of my old friends when I was walking in the street yesterday.
而while引导的主从复合句则通常都为延续性的动词，因而常常使用进行时态。
My mother was cooking while my father was watching TV.
One boy is rowing while the other boy in the boat is dangling around his
legs in the cool water of the lake.
一个男孩正在划船，而船里的另一个男孩则把腿悬垂在凉爽的湖水中。
2、when 可以用于 be about to do sth. when ...的固定结构当中
I was just about to call you when you called me.
3、while 可以表示对比关系“然而”
He is short while his brother is tall.
Tom has opened his own business while his classmates are still slogging
away at school.
当汤姆的同学还在学校苦读时，他已经开始了自己的事业。
4、while还可以引导让步状语从句“尽管”
While everyone else wouldn't go to the mountain area, he went without a
second thought.
温馨提示：
