具體你可以參考這一段.
when,while,as引導時間狀語從句的區(qū)別
when,while,as顯然都可以引導時間狀語從句,但用法區(qū)別非常大.
一、when可以和延續(xù)性動詞連用,也可以和短暫性動詞連用；而while和as只能和延續(xù)性動詞連用.
① Why do you want a new job when youve got such a good one already?（get為短暫性動詞）你已經找到如此好的工作,為何還想再找新的?
②Sorry,I was out when you called me．（call為短暫性動詞）對不起,你打電話時我剛好外出了.
③Strike while the iron is hot．（is為延續(xù)性動詞,表示一種持續(xù)的狀態(tài)）趁熱打鐵.
④ The students took notes as they listened．（listen為延續(xù)性動詞）學生們邊聽課邊做筆記.
二、when從句的謂語動詞可以在主句謂語動作之前、之后或同時發(fā)生；while和as從句的謂語動作必須是和主句謂語動作同時發(fā)生.
1．從句動作在主句動作前發(fā)生,只用 when.
①When he had finished his homework,he took a short rest．（finished先發(fā)生）當他完成作業(yè)后,他休息了一會兒.
②When I got to the airport,the guests had left．（got to后發(fā)生）當我趕到飛機場時,客人們已經離開了.
2．從句動作和主句動作同時發(fā)生,且從句動作為延續(xù)性動詞時,when,while,as都可使用.
①When ／While ／As we were dancing,a stranger came in．（dance為延續(xù)性動詞）當我們跳舞時,一位陌生人走了進來.
②When ／While ／As she was making a phonecall,I was writing a letter．（make為延續(xù)性動詞）當她在打電話時,我正在寫信.
3．當主句、從句動作同時進行,從句動作的時間概念淡化,而主要表示主句動作發(fā)生的背景或條件時,只能用 as.這時,as常表示“隨著……”；“一邊……,一邊……”之意.
① As the time went on,the weather got worse．（as表示“隨著……”之意）
② The atmosphere gets thinner and thinner as the height increases．隨著高度的增加,大氣越來越稀薄.
③As years go by,China is getting stronger and richer．隨著時間一年一年過去,中國變得越來越富強了.
④The little girls sang as they went．小姑娘們一邊走,一邊唱.
⑤The sad mother sat on the roadside,shouting as she was crying．傷心的媽媽坐在路邊,邊哭邊叫.
4．在將來時從句中,常用when,且從句須用一般時代替將來時.
①You shall borrow the book when I have finished reading it．在我讀完這本書后,你可以借閱.
②When the manager comes here for a visit next week,Ill talk with him about this．下周,經理來這參觀時,我會和他談談此事.
三、when用于表示“一……就……”的句型中（指過去的事情）.
sb．had hardly（＝scarcely） done sth．when．．．＝Hardly ／ Scarcely had sb．done sth．when．．．
①I had hardly ／scarcely closed my eyes when someone knocked at the door．＝Hardly ／ Scarcely had I closed my eyes when someone knocked at the door．我剛一閉上眼,就有人在敲門了.
②I had hardly ／scarcely entered my room when the telephone rang．＝Hardly ／Scarcely had I entered my room when the telephone rang．我剛一走進房門,電話就響了