while 后面接延续性行为,但这个动作肯定和主句动作时间不一样长.如：he was talking to me while he was watching the tv.应该说“看电视”比“谈话”时间长.而as通常两个动作一直相随,很可能时间相同.如：he was thinking of a question as watching the tv.这两个动作就是一直相随的.
as意为“一边……一边……”或“与……同时”,重在表示动作同时发生、伴随进行.while只指“时间段”,不指“时间点”,从句的动词只限于持续性动词.
1 从句表示"随时间推移"连词能用as,不用while.
As the day went on,the weather got worse.
日子一天天过去,天气越变越坏.
2 as引导短暂性动作的动词.
Just as I stopped my car,a man came up to me.