1．首先，as...as 是比较级，所以as long as 的意思是“像……一样长”，

否定结构是not so long as.

注意：long 既可以指“长度”，也可以指“时间”。例如： 

This line is four times as long as that one. 
      这条线是那条线的四倍长。
     My pencil is not so long as yours.
     我的钢笔没有你的长。 

You can keep the book as long as you like .
     这本书你愿意看多长时间都行。 

During the holidays , I like to stay in the countryside as long as I can .
    假期里，我想尽可能在农村多呆些时间。

2 . 表示条件，意思是“只要”。例如： 

As long as you tell truth , I”ll try to help you .
     只要你说实话，我会尽力帮助你。 

You may take this book away so long as you return it on time .
     只要你准时把书还回来，你可以拿走它。

3 . 表示原因，意思是“既然，由于，因为”。.例如： 

So long as the weather is changeable these days , we'd better get in wheat in time .
     因为近日天气可能变化，我们最好赶快收割麦子。 

So long as you are going to town tomorrow , you can do something for me .
     既然你明天到城里去，你可以为我做点事。

4、用法注意事项 

在多数情况下，as long as / so long as 意思相同，两者可以互换使用。

但下列情况下，通常只用as long as. 

(1) 在表示时间“长达…之久”时,往往用as long as。例如: 

They all continued their regard for me as long as they lived.
      他们毕生都在关心着我. 

For almost as long as Juanita could remember, climbing the hill seemed as easy as breathing, and as natural.
  在胡安妮塔的记忆中,爬山就如同呼吸一样简单而自然。 

(2) 在表示“既然,因为” 的含义时,多用as long as。例如: 

As long as we've driven this far, we might as well go on.
    我们既然已经驶得这么远了,就不妨继续前进. 

As long as you are here, go on.
    你既然已经来到这里了,就干吧.

5、更多实例

You can go out, as / so long as you promise to be back before 11 o'clock.
你可以出去,只要你答应在11点以前回来。 

I'll accept any job as / so long as I don't have to get up early.
只要不必早起,任何工作我都可以接受。 

--It's said it's going to turn colder and freeze later on.
听说过些时候天气要变冷,有冰冻.
--As long as it doesn't spoil the weekend.
只要不在周末就没事。 

I'm sure we are safe as long as(we are) in his care.
我深信只要在他的保护下,我们就会平安无事.

  义务教育英语课程标准五级词汇表(点击每一个单词，可直接链接到这个单词的用法.)