(1) be doing sth when … 正当

(引导从句，表示某事发生于另一活动、事件或情形期间)在…的过程中

It was raining when we arrived.


我们到的时候正在下雨。

He was still smiling when the door opened and his wife came in.


他正笑着的时候门突然开了，他妻子走了进来。


He was still smiling when the door opened and his wife came in.


他正笑着的时候门突然开了，他妻子走了进来。

When I met the Gills, I had been gardening for nearly ten years.

遇到吉尔一家时我已经做了近10年的园艺工作。


(2) be about to do sth …when …正要


We were about to start when it began to rain.我们刚要出发，天就开始下雨了。


(3)When it comes to…当提到

They are inexperienced when it comes to decorating

说到装修，他们就没有什么经验了。

《柯林斯高阶英汉双解学习词典》


When it comes to the superstar, the audience burst into cheers.当提到那个超级明星，观众中爆发出了欢呼声。

However, when it comes down to somebody that they know, they have a differentfeeling.

然而，涉及他们认识的人，他们的感觉就不同了。（这个 down看来是可以省略的）

《柯林斯高阶英汉双解学习词典》

When it comes to photography, I'm not an adept.

要说照相，我不是内行。

《汉英大词典》

When it comes to pop music we not only lead Europe, we lead the world.

我们不仅引领欧洲而且引领着全球的流行音乐潮流。

《柯林斯高阶英汉双解学习词典》


In the past we have heard only negatives when it came to following a healthy diet.

说到遵循健康饮食习惯，我们过去听到的都是否定的说法。

《柯林斯高阶英汉双解学习词典》

Few people, when it comes down to it, are so selfless.

说到底，很少有人能这样无私。

《柯林斯高阶英汉双解学习词典》（这个 down看来是可以省略的）


(4)When doing sth, 主语+谓语+宾语(表示两事同时发生)在…时，当…时


When crossing the streets, you should be more careful.

穿过街道的时候你应该小心。

When eating a whole cooked fish, you should never turn it over to get at the flesh on the other side...

吃一整条鱼时，切忌把它翻过来去吃另一面的肉。《柯林斯高阶英汉双解学习词典》


（5）had not done sth --- when ---/ hardly --- when ---


He had not fallen asleep when the telephone rang.
他刚要入睡电话就响了。


hardly、scarcely和barely与when连用，表示刚…就…

We had hardly/scarcely/barely sat down at the table, when the phone rang.

我们刚在桌子旁坐下，电话铃就响了。


Hardly/Scarcely had we sat down at the table, when the phone rang.

我们刚在桌子旁坐下，电话铃就响了。

在正式的书面英语中，尤其在文学体中，上述各词可置于句首，然后将主语和动词的位置倒装。

注意：在这类句子中通常用when而非than，亦可用before：

I scarcely had time to ring the bell before the door opened.

我刚一按门铃，门就开了。


(6) had just done ---- when ---
　例：I had just gone to bed after a very hard day when the phone rang. 在劳累了一天之后我刚刚就寝，电话铃就响了。


He had just drifted off to sleep when the phone rang.

他刚睡着电话铃就响了。

（7）引导条件状语从句，意思是“如果”，相当于if。例如：

Call me at once when anything goes wrong with the computer.如果计算机发生故障，立即叫我。

I'll start to think about it when I have to write my report.

我要写报告时会对此予以考虑的。

《柯林斯高阶英汉双解学习词典》

When you have got a handle on your anxiety you can begin to control it.

一旦了解了自己焦虑的原因，你就开始能控制它了。

《柯林斯高阶英汉双解学习词典》

Turn off the switch when anything goes wrong with the device.


如果装置出故障，就把开关关掉。