L1A(first language acquisition)is expected to shed light on the L2(second language)teaching.However,how far L1A correlates with second language teaching is an argument that never ends.Hence,the hypotheses on L1A and its connection with L2 Teaching are analyzed,along with a discussion on the relationship between L1A,L2A and L2 Teaching.The limitation of L1A to L2T is elaborated from the aspect of literacy,age and time distinction.