【Abstract】The Critical Period Hypothesis believe that the younger the learner is，， the better he or she can master the language. Based on the Critical Period Hypothesis and empirical research， the author points out that learner at different ages have their own advantage to master English. It is untrue to learn a language as early as possible. Thus Critical Period Hypothesis is proved of one-side view. The author suggests that school should make different right teaching plans， according to different advantages at different ages. Finally， the author provides some suggestions and strategies on school English education in the context of China.
　　【Key words】Critical Period Hypothesis； second language acquisition； school English teaching
　　1. The explanation of Critical period Hypothesis
　　The biologist Penfield and Robert are the forerunner of the Critical Period Hypothesis. They stated （1959）： at the certain age of the life， one can acquire a language easily and quickly without external interruption and in no need of being taught. This opinion was accepted by Lennebery， who put forward the Critical Period Hypothesis in his book Biological Foundation of Language. He stated that language was the product of the brain. The development of the language ability was controlled strictly by the human physiology. At the age of 2 to the puberty， that is from 2 years to 12 years old， language can be acquire naturally and effortlessly because of the brain plasticity. But after the puberty， the brain develops fully and the neurological system loses such plastic icy， making the language acquisition harder and harder.（Lennebery 1967： 176）
　　1.1 The supporters of Critical period Hypothesis and their researches
　　Many researches were done to support Lennebery’s Critical Period Hypothesis. That is， many learners believed that the children who learn a second language before the puberty have more advantages than those who start to learn it after puberty.
　　In the late 1960 s， Asher and Garcia investigated the pronunciation of Cuban immigrates between the ages of 7 and 19 in the United States， finding only those who were under 6 when they got to the United States have a more near-native speech of Americans than the others. In 1976， Oyama took 60 Italians immigrants between the ages of 6 years old to 20 years old in the United States. After 5 years to 18 years living in the United States， they were asked to finish a task of reading loudly and free talk. At the same time， two Native American adults were asked to assess their native ness. It is discovered from this research that children who were under 6 when they arrived in America have a higher probability of acquiring a near-native pronunciation of English than those older than 13 years old.