Like Simple Future, Future in the Past has two different forms in English: "would" and "was going to." Although the two forms can sometimes be used interchangeably, they often express two different meanings.
就如般将来时，一般过去将来时有两种不同的形式：“would”和“was going to”。虽然这两个形式偶尔可以互换，但一般来说是表达不同意思的。
[would + VERB]
[would + 动词]
I knew you would help him.
FORM Was/Were Going To
形式Was/Were Going To
[was/were + going to + VERB]
[was/were + going to + 动词]
I knew you were going to go to the party.
Future in the Past is used to express the idea that in the past you thought something would happen in the future. It does not matter if you are correct or not. Future in the Past follows the same basic rules as the Simple Future. "Would" is used to volunteer or promise, and "was going to" is used to plan. Moreover, both forms can be used to make predictions about the future.
一般过去将来时常用于描述过去某时间里你对于未来的想法。猜想正确与否并无多大关系。一般过去将来时和一般将来时的基本规则一样。“would”用于描述志愿或允诺。“was going to”常用于描述计划。此外，两种形式都可用于描述对未来的猜想。
I told you he was going to come to the party. (plan)
I knew Julie would make dinner. (voluntary action)
Jane said Sam was going to bring his sister with him, but he came alone. (plan)
I had a feeling that the vacation was going to be a disaster. (Prediction)
He promised he would send a postcard from Egypt. (Promise)