形式主语句型是英语中一种常见的句型结构，其中 “it”作为形式主语，而真正的主语通常是一个从句或不定式短语。这种结构在表达观点、时间、距离、内容等时非常有用。以下是一些常见的形式主语句型：
It + be + 形容词 + to do sth.
例句：It is important to learn a foreign language.
It + be + 形容词 + doing sth.
例句：It is nice talking to you.
It + be + 名词 + doing sth.
例句：It is no good telling lies.
It + be + 不定式/动名词
例句：It took me three days to get there on foot.
It + be + 形容词 + （for/of + sb.） + 不定式
例句：It is very important for you to work hard.
It + be + a + 名词 + 主语从句
例句：It is a pity that he missed the chance.
It + be + no + 名词 + to do sth.
例句：It is no use crying over spilt milk.
It + be + 形容词/名词/动词 + that/who ...
例句：It is clear that he is not responsible for the mistake.
It is not until + 被强调部分 + that ...
例句：It was not until she took off her dark glasses that I realized she was a famous film star.
这些句型结构在英语中非常常见，掌握它们有助于提高写作和口语表达的准确性和流畅性。建议在实际应用中根据具体的语境选择合适的句型结构。