From the theory of language acquisition teachers can enlighten themselves to optimize the teaching method as possible so as to improve the college students' English ability.The use of unfit teaching method is one of the reasons that cause the phenomenon that college English Teaching takes a lot of time with low effect.It is beneficial to understand second language acquisition and to investigate the superior teaching method from the theory of language acquisition theorized by Stephen Krashen.Also it is vital to create the teaching environment that can promote language acquisition and to make the teaching method match the teaching aim best so as to lower the " cost of teaching " and enlarge the " effective output of teaching".