be to do是英语中关于将来时表示的一种：

 be( am / is / are ) + 不定式表示方法描述两种情况：
①按计划安排要发生的动作，这个动作发生的时间一般不会很远；②要求或命令他人做某事。

A) The new bridge is to open to traffic in three days.

新桥三天后通车。
The factory is to go into production before National Day.

这家工厂国庆节前投产。

We are to discuss the report next Saturday.

我们下周六讨论这个报告。
B) You are not to bring any mobile communication means into the exam-room.

任何移动通讯工具都不得带入考场。
You are to stay home until your mother comes back.

你妈回来之前你不要出去。

类似的短语表示将来的还有：

be( am / is / are ) + going +不定式
这种表示方法主要是说明

A）说话人的意图、打算；

B）某种可能性（有迹象要发生的事）；

C）计划，安排要发生的事。例如：

A) He is going to spend his holidays in London.

他打算在伦敦度假。
Who is going to speak first? 谁先发言？

What are you going to do tomorrow?

你明天打算干什么？
B) It is going to rain soon .马上要下雨了。

Look at the dark clouds, there is going to be a storm
看天山乌云翻滚，暴风雨就要来了。
Is he going to collect any data for us?

他会帮我们收集资料吗？
If you go to New Zealand, you are going to like the place.

如果你去新西兰，你会喜欢上那个地方的。

C）The play is going to be produced next month。
这部戏剧下月就会制作好。

We are going to have a volleyball` match tomorrow. 明天我们将举行排球比赛。

be about to＋动词不定式表示“马上做某事”

be due to＋动词不定式表示预先确定了的事，必定发生的事

He is about to leave for Beijing.

他马上要去北京。

The train is due to depart in ten minutes.

火车定于十分钟后发车。

Don’t go out. We’re about to have dinner. 

别出去了，我们很快就吃饭。

I was about to start when it began to rain. 

我们刚要出发就下起雨来。

注意：be about to 不能与tomorrow, next week 等表示明确将来时的时间状语连用。