(1) 在but, except, than, as 和动词be之后，人称代词可用主格,亦可用宾格(在口语中常用宾格)。如:Nobody but I /me has known it. 除了我没人知道。I'm thinner than she/her.我比她瘦。-Who is knocking at the door?谁在敲门?It's I /me.是我。
(2) 人称代词 it 可指天气、时间、自然现象、距离、重量、价格等。如:It's going to rain. 要下雨了。(指天气)；It's about ten minutes' walk. 步行大约十分钟的路程。(指路程)
(3) it还常作形式主语或形式宾语。如:It's necessary for us to drink at least eight cups of water everyday.我们有必要每天至少喝八杯水。(形式主语)；I find it difficult to learn English well. 我发现学好英语很难。(形式宾语)
(4) 指代不明确的人。当说话者不清楚或没有必要知道说话对象的性别时，用 it 指代。如:-John, someone in your class phoned you this morning. 约翰，今天早晨你班有人给你打了电话。-Oh,who is it? 噢，是谁?It's a lovely baby. Is it a boy or a girl? 宝宝真可爱。是男孩还是女孩?
(5) 指代国家、都市、船舶的名词，含有感情色彩时常用 she 。如:China will always do what she has promised. 中国总是言出必行。Titanic was once the biggest ship. She was great!泰坦尼克号曾是世界上最大的轮船。她真是太棒了!
