Vocabulary in any language is a complex system. Groups of words with synonymous relationship are known as synonyms. A language with a long history has rich vocabulary. English is extremely rich in synonyms because of historical reasons. Each group of synonyms has the same or very close basic meaning. That’s the basis of forming synonyms.The discrimination of synonyms plays an important role in communication and expression of ideas. It can improve one’s language ability such as reading, writing and speaking. It can have different expressions of objective things and avoid repetition of the same word. So it can make the English conversation and writing more lively. It can avoid expressing too frankly. The correct use of synonyms can have a better effect on modification.