Interlanguage,which functions as a relatively systematic transition from initial knowledge of a language to native proficiency during the process of language acquisition,is always regarded as an unstable set of language characteristics produced by learners.Its fossilization is a universal phenomenon in SLA and it derives from multiple factors.Through the research into interlanguage and its fossilization,we should hold a totally different view from traditional one on the nature and function of learner language,and resort the significance of the research to guiding SLA.Especially,for English teaching in China,we will present some crucial issues that we should not ignore,involving teacher's training,teaching materials and the handling of learner's errors,etc.
