It的用法及其句型和固定搭配，是英语语法的重点、难点，也是高考的热点。
01、It 指情形、行为等That’s just it — I can’t work when you’re making so much noise.
原因就在这里 —— 你弄出这么大的声音, 我工作不了。
His mother warned him never to go to the Internet cafe, but it didn’t work.
他妈妈告诫他不要去网吧，但毫无用处。
02、 It指人(未知的人或婴儿)— Someone is knocking at the door; go and see who it is.
有人敲门，去看看是谁?
— It must be the milkman.
一定是送奶工。
What a beautiful baby — is it a girl?
多么好看的婴儿啊, 她是女孩吗？
03、 It指环境，情况等If it’s convenient, I can see you tomorrow.
要是方便的话, 我明天可以见你。
It’s getting very competitive in the car industry.
汽车工业方面的竞争日益加剧。
04、 It作形式主语当动词不定式或that从句充当主语时，把主语移到句尾，用it来填补正常的主语位置。在这种情况下，it称之为形式主语，后移成分为后移主语或真实主语。例如：
It’s surprising that he should have passed the test.
It’s a pity / shame that he should ask for money from a foreigner.
It worried her a bit that her hair was turning grey.
It was believed that the earth was flat in the old times. (=The earth was believed to be flat in the old times.)
It will take them more than ten years to complete the project.
05、 It作形式宾语It作形式宾语，可以指代后面真正的宾语。例如：
He feels it his duty to help others. 他感觉帮助他人是他的责任。
Do you think it possible for them to send an engineer there? 你认为可能给他们派一个工程师去那里吗？
She finds it boring staying / to stay at home. 她觉得待在家中很无聊。
I don’t like it when he speaks with his mouth full of food. 我不喜欢他满嘴含着食物讲话。
I would appreciate it if you can lend me a hand. 如果你能帮我的忙，我将非常感激。
06、 强调句型结构为：It is / was 被强调部分 that (who)…。强调句型用来强调谓语动词以外的任何句子成分。当被强调部分是人时，也可以用who。
在使用强调句型时需注意以下几点：
(1) 请注意强调句型的特殊疑问句；
When was it that he got back home?
Where was it that you came across him?
(2) 在强调原因状语从句时，只能强调由because所引导的从句；
It was because it kept on raining for days that we could not carry out our plan.
(3) 在强调not …until结构时必须把not与until一起放到被强调的位置上；
It was not until his hometown was liberated that he was able to go to school.
(4) 注意强调句型与定语从句的区别；
It is novels that Miss Green enjoys reading.
格林小姐喜欢读的是小说。 ( 强调句 )
It is a question that needs careful consideration.
这是一个需要仔细考虑的问题。 ( 定语从句 )
(5) 注意区分强调句型的 it与表示时间的it。
It was nine o’clock when he returned home last night. (表时间)
It was at nine o’clock that he returned home last night. (强调句型)
