In foreign language teaching,it has always been found that there are many language learners whose second language(L2)level remains stagnant or even becomes worse no matter how hard they try.However,this may not relate to their attention given to language but to interlanguage fossilization,which results from various causes,is ubiquitous in second language acquisition(SLA)and foreign language learning.This paper,based on the empirical evidence of language learning and acquisition,probes into the nature and characteristics of interlanguage,analyzes the main causes of fossilization,and discusses pedagogical implications for avoiding fossilization in English language learning.