when的用法小結如下:
一、when 意為“當…時”,用作連詞,引導時間狀語從句,從句的謂語動詞可以是延續的（此時相當於while）,也可以是非延續性的.引導的時間狀語從句通常用現在時表將來.
I will write to my sister when I have finished the book.我讀完這本書後便給姐姐寫信.
When he sees the photo,he can"t help thinking of his childhood.
每當看到這張照片,他就不禁想起童年.
二、when 引導時間狀語時,若主從句主語一致或從句主語為it且從句謂語動詞含be的形式,可省略從句的主語及be 部分.
When (I was) walking on the street,I came across Mary.我在街上漫步時遇上了瑪麗.
He gave good practical advice when (he was) asked.他有求必應,給出了好的可行性建議.
三、when用作連詞,表突然發生某事,意為“就在這時/那時”（=at this/that time）,常構成句型 be doing… when… 或be about to do…/be on the point of doing… when….
I was just coming along to see you when I ran into Tom.遇見湯姆時,我正在來看你的路上.
He was about to go to bed when the telephone rang.他準備睡覺時電話鈴響了.
四、When用作連詞表過早發生某事,意為“還沒（剛剛）…就”,可構成句型 hardly/scarcely…when….使用該句型時應注意兩點：① 主句的謂語動詞用過去完成時,從句謂語動詞用過去時.② 若hardly/scarcely 位於句首時,其後的句子部分倒裝,而when引導的從句不倒裝.
I had been there little more than a week when I set to work in earnest.
我在那還不到一個星期就開始認真工作.
Hardly had I opened the door when he hit me.我一開啟門他就撞了我.
六、when引導條件狀語從句,意為“在…情況下；如果；要是”,相當if.
Why do you walk when you have a car?你有車為什麼還走路呢?
No one can make a dress when they haven"t learnt.沒有人能夠不學就能製作衣服的.
七、when 引導時間狀語從句,意為“一…就 …”,相當於 as soon as .
We will start when everything is ready.一切準備好了我們就出發.
When she comes,I will give it to her.她來了我就給她.
八、when可引導原因狀語從句,意為“既然；考慮到…”,相當於since,as 或now that.
You can"t go home when you haven"t finished your work.
既然你沒完成工作,你就不可以回家.
九、when可引導名詞性從句或接不定式.
Could you tell me when you will leave for Shanghai?能告訴我你什麼時候去上海嗎?
Ask him when to open it.告訴他什麼時候開啟.
十、when作關係副詞,引導定語從句,在從句中充當時間狀語.
At the time when I saw him,he was very well.我見到他時他很好.
Sunday is a holiday,when people do not go to work.星期天是一個假日,這天人們不用去上班.
when的用法小結如下:
一、when 意為“當…時”,用作連詞,引導時間狀語從句,從句的謂語動詞可以是延續的（此時相當於while）,也可以是非延續性的.引導的時間狀語從句通常用現在時表將來.
I will write to my sister when I have finished the book.我讀完這本書後便給姐姐寫信.
When he sees the photo,he can"t help thinking of his childhood.
每當看到這張照片,他就不禁想起童年.
二、when 引導時間狀語時,若主從句主語一致或從句主語為it且從句謂語動詞含be的形式,可省略從句的主語及be 部分.
When (I was) walking on the street,I came across Mary.我在街上漫步時遇上了瑪麗.
He gave good practical advice when (he was) asked.他有求必應,給出了好的可行性建議.
三、when用作連詞,表突然發生某事,意為“就在這時/那時”（=at this/that time）,常構成句型 be doing… when… 或be about to do…/be on the point of doing… when….
I was just coming along to see you when I ran into Tom.遇見湯姆時,我正在來看你的路上.
He was about to go to bed when the telephone rang.他準備睡覺時電話鈴響了.
四、When用作連詞表過早發生某事,意為“還沒（剛剛）…就”,可構成句型 hardly/scarcely…when….使用該句型時應注意兩點：① 主句的謂語動詞用過去完成時,從句謂語動詞用過去時.② 若hardly/scarcely 位於句首時,其後的句子部分倒裝,而when引導的從句不倒裝.
I had been there little more than a week when I set to work in earnest.
我在那還不到一個星期就開始認真工作.
Hardly had I opened the door when he hit me.我一開啟門他就撞了我.
六、when引導條件狀語從句,意為“在…情況下；如果；要是”,相當if.
Why do you walk when you have a car?你有車為什麼還走路呢?
No one can make a dress when they haven"t learnt.沒有人能夠不學就能製作衣服的.
七、when 引導時間狀語從句,意為“一…就 …”,相當於 as soon as .
We will start when everything is ready.一切準備好了我們就出發.
When she comes,I will give it to her.她來了我就給她.
八、when可引導原因狀語從句,意為“既然；考慮到…”,相當於since,as 或now that.
You can"t go home when you haven"t finished your work.
既然你沒完成工作,你就不可以回家.
九、when可引導名詞性從句或接不定式.
Could you tell me when you will leave for Shanghai?能告訴我你什麼時候去上海嗎?
Ask him when to open it.告訴他什麼時候開啟.
十、when作關係副詞,引導定語從句,在從句中充當時間狀語.
At the time when I saw him,he was very well.我見到他時他很好.
Sunday is a holiday,when people do not go to work.星期天是一個假日,這天人們不用去上班.