While
1while通常表示一段时间，从句中宜用持续性动词作谓语。e.g. Strike while the iron is hot.趁热打铁。
She fell asleep while she was reading the newspaper.她在看报的时候睡着了。
②while有时可以作并列连词,表示对比,可译成“而”。e.g.I am fond of English while he likes maths.
我喜欢英语而他却喜欢数学。

As
as表示点时间时，从句中用短暂性动词:表示段时间时，用持续性动词。as和when两者经常可以通用。
e.g. The thief was caught as/ when he was stealing in the
supermarket.小偷在超市行窃时被逮住了。
2as表示一边.....一边.....，强调从句和主句中两个动作交替进行或同步进行。
e.g. They talked as they walked.他们边走边聊。
He looked behind from time to time as he went.他一边走，一边不时地往后看。
3as表示随着
e.g. As time goes on, it's getting warmer and warmer.
随着时间的推移,天气变得越来越暖了。