下面是小编搜集整理分享的高中英语语法it的用法，一起来看看吧。
It用法及其句型和固定搭配，是高中英语语法的重点、难点，又是高考英语的热点，因此应给予充分的重视，现将it用法归纳如下：
一、作人称代词
1、it代替前面(或后面)的单数名词或分句等所表示的事物。
e.g. You cannot eat your cake but have it.(it代替前面的cake)Although we cannot see it, there is air all around us. (it代替后面的air)They say he has left town, but I don’t believe it. (it代替前面They…town分句中的情况)
2、代替有生命但不能或不必分阴阳性的东西(包括婴儿)。
e.g. Yesterday we saw a big tree. It was fully twenty metres high. (it代替前面的tree)The baby cried because it was hungry. (it代替前面的baby)
3、在某些习惯说法中，可以代替人。
e.g. -- Someone is knocking at the door, Peter. -- Who is it? -- It’s me.
-- Who are singing? -- It is the children.
-- The light is still on in the lab. It must be the third-year students doing the experiment.
4、it与one的区别：这两个词都可以代表前面说过的名词，但it用于同名同物的场合;one则用于同名异物的场合。
e.g. -- Do you still have the bicycle? -- No, I have sold it.
-- Is this knife yours? -- No. It is Xiao Zhang’s. Mine is the one on the desk.
5、it与that的区别：两词都可代替某一特定名词，但that指同一类，并非同一个。
e.g. The climate of South China is mild(温和的); I like it very much.(it指the climate of South China)The climate of South China is much better than that of Japan.(that指the climate)
二、作无人称代词it作无人称代词时，除了句中找不到它所代表的词语外，另一个特点是它后面的内容都是表示天气、时间、距离、度量衡及情况等。
It is fine (rainy, windy, etc.).
It is noon.
It is a half hour’s walk to the factory.
It is eighteen square metres in area.
What does it matter?
三、作强调词，构成强调结构用以帮助改变句子结构，使句子的某一成分受到强调。“It is (was) + 所强调的成分+ that (who) + 其它成分。”在这个句型中，it本身没有词义。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例When was it that he changed his mind to take part in the activity?
2. 在强调原因状语从句时，只能强调由because所引导的从句例It was because he was ill that he didn't come to school yesterday.
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例It was not until she took off her dark glasses that I realized she was my brother.
4. 注意强调句型与定语从句的区别例It was at 7 o'clock that he came here yesterday.( 强调句型)It was 7 o'clock when he came here yesterday.(定语从句)四、It用作形式主语It替代作主语的从句、动词不定式、动名词，而把真正作主语的从句、动词不定式、动名词置于句尾。