be +動詞不定式（即be + to do sth.）的用法如下：
1.表示按計劃或安排要做的事.例如：
When are you to leave for home?你什么時候回家?
She is to be married next month.她將于下個月結(jié)婚.
The Queen is to visit Japan in a week’s time.女王將于一周后訪問日本.
這種結(jié)構(gòu)也可用于過去.was / were to do sth.表示曾經(jīng)計劃要做的事,但不表明計劃是否被執(zhí)行,或表示“命運（即命中注定要發(fā)生的事）”,而非計劃；was / were to have done sth.表示未曾實現(xiàn)的計劃.例如：
I felt nervous because I was soon to leave home for the first time.我感到很緊張,因為我很快就要首次離開家了.
They said goodbye,little knowing that they were never to meet again.他們告了別,不知道以后再也不會見面了.
We were to have told you,but you were not in.我們本來想告訴你的,但是你不在家.
（你看這里）2.表示“應該”,相當于should,ought to.例如：
You are to report to the police.你應該報警.
What is to be done?應該怎么辦呢?
3.表示“必須”,相當于must,have to.例如：
The letter is to be handed to him in person.這封信必須親手交給他.
You are to do your homework before you watch TV.看電視之前你得先做完作業(yè).
4.表示“想,打算”,相當于intend,want.例如：
If we are to be there before ten,we’ll have to go now.如果我們要在十點前到,我們現(xiàn)在就得走.
5.用于第一人稱疑問句,表示征求對方意見.例如：
Am I to go on with the work?要我繼續(xù)完成這項工作嗎?
What are we to do next?我們下一步該怎么辦?
6.用于否定句,表示“禁止”,相當于mustn’t.例如：
The books in this room are not to be taken outside.這個室內(nèi)的書籍不得帶出室外.
You are not to smoke in the reading-room.你不可以在閱覽室里吸煙.
7.表示“可以,可能”,相當于may,can.例如：
The news is to be found in the evening paper.這條消息可以在晚報上見到.
Such people are to be found everywhere.這種人到處都有.
She is nowhere to be found.在哪里也找不著她.
8.were to do sth.用于if或even if / even though從句中,表示對未來的假設.例如：
If I were to tell you that I killed him,would you believe me?要是我告訴你是我殺了他,你會相信嗎?
Even if the sun were to rise in the west,I would never do such a thing.即使太陽從西邊出來,我也決不做這種事.
9.be to blame(該受責備,對某壞事應負責任)與be to let(待出租)兩種結(jié)構(gòu)中,用不定式的主動形式表示被動含義.例如：
Which driver is to blame for the accident?這事故是哪個司機的責任?
This house is to let.這房子要出租.