關于這個問題,請參考《中學英語高頻詞詳解詞典》（金盾出版社）,這是我見過的最好,最詳細的說明,特與你分享：
Until用法詳解
表示“直到……為止”,兩者常可換用,只是 until 比 till稍正式,所以在正式文體中,一般用 until,而在口語或非正式文體中則兩者都可用.從其后所接成分來看,till多與名詞或較短的從句連用,而較長較復雜的成分多用 until,位于句首時也多用 until.兩者在用法上應注意以下幾點：
1.相關主句謂語必須是持續(xù)性動詞,若是終止性動詞,則應為否定式（因為終上性動詞一旦被否定就成為狀態(tài),便可持續(xù)）.如：
He waited until she was about to leave.他等著一直到她準備離開.
She didn’t marry until she was over fifty.她直到50多歲才結婚.
2.引導時間狀語從句時,其謂語要用現(xiàn)在時表示將來意義.如：
I won’t leave until he comes back tomorrow.我要等他明天回來后再走.
Continue in this direction until you see a sign.一直朝著這個方向走就看見指示牌了.
3.有時其后可跟副詞或介詞短語等.如：
He has been ill until recently.他最近一直生病.
Until when are you going to stay here?你在這兒要待到什么時候?
We didn’t eat till past midnight.直到午夜過后我們才吃飯.
She won’t go home until after the exam.她要考完試之后再回家.
如果語境的需要,有時甚至可以接帶有“引導詞”的從句.如：
Don’t leave until after I’ve spoken to you.我和你說完后再離開.
4.用于 not…until [till]…結構
(1) 若主句動詞為終止性動詞,其意為“直到……才……”；若主句為持續(xù)性動詞,其意為“不到……就……”.比較：
They didn’t find her till the next day.他們直到第二天才找到她.
He didn’t wait until I returned.他沒等到我回來（沒等我回來他就走了）.
有時 until 或 till 可以換成 before.如：
Until [Before] you told me,I had no idea of it.在你告訴我之前,我對此一無所知.（即直到你告訴我,我才知道）
(2) 可用于It is (was) not until [till]…that…這樣的強調句型.如：
It was not until I met you that I knew real happiness.直到我遇到你以后,我才真正體會到幸福.
It was not until she took off her dark glasses that I realized she was a famous film star.直到她取下墨鏡,我才意識到她是一位著名影星.
(3) 若將not until [till]置于句首,其后的主句要用倒裝語序.如：
Not until much later did she learn who her real father was.她很久以后才知道她真正的父親是誰.
Not until he received her letter did he fully understand the depth of her feelings.他直到收到她的信之后才充分理解她的感情有多深.