一、before long意为“不久” 、“很快” “立刻，马上”(=soon，a little later)， 就是一个固定短语，可用于将来、现在或过去时态。
如:
We'll be home before long.
我们很快就要到家了。
We'll know before long.
我们很快就会知道了。
German interest rates will come down before long
德国的利率水平很快就会降下来。
I hope to see you again before long.我希望不久能再见到你。
Before long he came to a small village.不久他来到了一个小村庄。
Before long he took over the editing of the magazine.
他不久就接手负责杂志的编辑工作。
Before too long he started involving me in the more confidential aspects of the job.
不久，他便开始让我介入工作中更机密的方面。
“I have enjoyed my visit very much.”“We hope to see you again before very long.”
“我很享受这次访问。”“我们希望不久能再次见到你。”（托福真题）
以上二例说明before long中间可以插入一个修饰语，加强一种语气。
二、long before的用法应注意以下几点:
(1)单独使用，相当于一个副词，表示比过去某时早得多的时间，意为“老早”、“很久以前”“早就”等，通常与过去完成时连用。
如:
We've seen that film long before.
我们早就看过那部电影了。
That had happened long before.
那是很早以前的事了。
She had left long before.她老早就离开了。
That had happened long before.那事老早就发生了。
I had known her long before.
很久以前我就认识她。
比较: long ago意为“很久以前”，通常与一般过去时连用:
I met him long ago.我很久以前就认识他了。
We met once long ago.我摸很久以前就认识。The house was pulled down long ago.
那栋房子很久以前就被拆掉了。
If it had been left to me I would have put him out on the street long ago.
换了我，早就把他赶出家门了。
Harry's daughter is dead. She died long ago.
哈里的女儿已不在人世，很久以前就死了。
I learned long ago to avoid these invitations
我很早就学会怎样躲开这种邀请了。
He should have come home long ago.
论理他早该回家了。
The two parties reached a secret agreement long ago.
双方早有默契。
He left long ago.
他早走了。
The spring dried up long ago.
这泉水早就干涸了。
I knew long ago that the two of them wouldn't make it together.
我早就料到他俩的事要吹台（落空）。
It was on TV not long ago.
电视不久以前播出了这个节目。
I told them that long ago.
我早已告诉他们了。
Had it not been for his family, He'd have gone away long ago.
要是没有家眷拖累，他早就远走高飞了。
(2)后接名词或句子，相当于一个介词或连词；意为“在....的很久以前”、“早在...以前”，“在……之前已很长时间，早就”等。如:
He retired long before the war.
他在战争之前早就退休了。
Long before her death in 1886, the poet Emily Dickinson had become a legend in her hometown of Amherst Massachusetts.
在1886年去世之前，诗人艾米丽·狄金森早就在她的家乡马萨诸塞州的阿默斯特成为了一个传奇人物。（托福真题）
The plot to assassinate Martin Luther King had started long before he was actually killed.
刺杀马丁·路德·金的计划在实施前酝酿已久。
She had left long before his return [he returned].
在他回来的很久以前她就走了。
He had worked in the factory long before he got married.
在他还没有结婚的很久以前他就在这家工厂工作了。
此时的主句谓语也可用一般过去时(因为before 已体现了动作的先后关系)。如:
This happened long before you were born.这事在你还没出生以前很久就发生了。
He was very excited, and it was long before he calmed down.
他很激动，心情久久不能平静。
Long before I ever went there, Africa was alive in my imagination.
早在我真正踏足之前很久，非洲就已在我的脑海中活灵活现了。
(3)用于It is long before..,肯定句型中是“过了很久才……”，否定句中表示“不久，或没过多久……”。如:
It was long before he came back.过了好久他才回来。
He was very excited, and it was long before he calmed down.
他很激动，心情久久不能平静。
It won't be long before we see each other.不久我们又会见面的。
It was not long before the news was widely circulated.
这个消息不久就哄传开了。
It was not long before I realised the enormity of my faux pas.
没过多久，我就意识到自己有多么失态。
It will not be long before the inflation figure starts to fall
过不了多久，通货膨胀率就会开始下降。
同义句比较:
Before long he went to Paris.不久他就去了巴黎。
=lt wasn't long before he went to Paris.不久他就去了巴黎。