as far as的用法如下：
1. 用于本义，意为“与……一样远”“一直到……” (在否定句中也可用 so far as)。如：
We walked as far as the river. 我们一直走到河边。
We didn’t go as [so] far as the others. 我们走得不如其他人远。
I’ve read as far as the third chapter. 我已读到第三章。
2. 用于引申义，意为“就……而言”“从……来看”“尽……所能”“只要”(有时可用 so far as)。如：
We’ll help you as far as is possible. 我们会尽可能帮你。
As [So] far as I know, that is highly unlikely. 就我所知，那是极不可能的。
As [So] far as I can see, there are no mistakes. 据我看 没有什么差错。