一）在后面加s。如：fathers, books, Americans, Germans, apples, bananas

二）x, sh, ch, s, tch后加es。如：boxes, glasses, dresses, watches, wishes, faxes

三）1）以辅音字母加y结尾的变y为i再加es　如：baby-babies, family-families, duty-duties, comedy-comedies, documentary-documentaries, story-stories

2）以元音字母加y结尾的直接加s。如：day-days, boy-boys, toy-toys, key-keys, ways

四）以o结尾加s（外来词）。如：radios, photos, 但如是辅音加o的加es：如: tomatoes西红柿, potatoes马铃薯

五）以f或fe结尾的变f为v再加es(s)。如：knife-knives, wife-wives, half-halves, shelf-shelves, leaf-leaves, yourself-yourselves

六）单复数相同（不变的）有：fish, sheep, deer鹿子, Chinese, Japanese

七）一般只有复数，没有单数的有：people, pants, shorts, shoes, glasses, gloves, clothes, socks

八）单词形式不变，既可以是单数也可以是复数的有：police警察局，警察, class班，同学, family家，家庭成员

九）合成的复数一般只加主要名词，多数为后一个单词。如：action movie-action movies, pen pal-pen pals; 但如果是由man或woman所组成的合成词的复数则同时为复数。如：man doctor-men doctors, woman teacher-women teachers

十）有的单复数意思不同。如：fish鱼 fishes鱼的种类, paper纸 papers报纸，卷子，论文, work工作 works作品，工厂, glass玻璃 glasses玻璃杯，眼镜,　orange桔子水 oranges橙子, light光线 lights灯, people人 peoples民族,　time时间 times时代, 次数, chicken 鸡肉　chickens 小鸡