In English grammar, the future-in-the-past is the use of would or was/were going to to refer to the future from the perspective of some point in the past.
在英語語法里，一般過去將來時使用would或was/were going to去描述過去某個時間點對未來的看法。

The simple future is a form of the verb that refers to an action or event that has not yet begun. The simple future is also used to make a prediction or to show ability, intention, or determination.
一般將來時描述未來一個還未發(fā)生的動作或事件。一般將來時也用于預(yù)測或展現(xiàn)能力、目的和決心。

Examples：
例子：

（1）

Last month, when he knew that we were going to divorce, he said that it was the best decision.
上個月，當他知道我們要離婚，他說這是最好的決定。

We are going to divorce next month.
我們下個月離婚。

（2）

I was going to tell him, but he didn't give me a chance.
我想要告訴他這些事的，但他沒給我機會。

I will tell him everything tonight.
我今晚會告訴他所有事。

（3）

I thought we were going to eat out tonight.
我想我們今晚會出去吃。（過去想的）

I think we are going to eat out tonight.
我想我們今晚會出去吃。

（4）

He said that he wouldn't finish his work this afternoon.
他說他今天下午完成不了工作。（過去說的）

He says that he won't finish his work this afternoon.
他說他今天下午完成不了工作。

（5）

Last Sunday we were going to visit the Great Wall, but it rained.
上星期天我們本想去游覽長城的，但卻下雨了。

We are going to visit the Great Wall tomorrow.
我們明天去游覽長城。

對比一下是不是很簡單？同樣都是描述未來，只需要分辨描述未來的那番話是過去說的，還是此時說的就可以了。