【Abstract】Redundancy is a language phenomenon that appears in every level of language and it is internal to language. This paper attempts to explain the forms and functions of redundancy through different levels of language with several examples， thus the value of redundancy is pursuit to help learners to obtain a deeper and better understanding in language learning.
　　【Key words】redundancy； ambiguity； comprehension
　　【作者簡介】马文星，女，甘肃庆阳人，西安外国语大学英文学院，2017级在读研究生，研究方向：外国语言学及应用语言学。
　　1. Introduction
　　In linguistics， redundancy refers to information that is expressed more than once. Redundancy by definitions from various scholars are noted as： “information available for more than one source” （Smith， 1971：132）； or redundancy is a critical feature in our communication and language in particular. （Darian， 1979）. According to the definition， many people regard redundancy as a negative feature of language， but it does make a difference in a particular way to forming human language.
　　2. Forms of the redundancy
　　In previous we mentioned redundancy exists in all level of language， and the types of the redundancy are divided into grammatical redundancy and contextual redundancy because the two could incorporate all kinds of redundancy.
　　2.1 Grammatical redundancy
　　Grammatical redundancy refers to a internal system and the rule manipulating language in which two or more of its forms that serve the same function. （Wit