The theory of SLA is a scientific enquiry to the second language study,which in China mainly refers to the study of English.Due to different perspectives of SLA,the study tends to be interdisciplinary.The paper focuses on the learners'subjective differences,that is,individual differences,exploring how the learners'individual differences reflect in the SLA and how such differences are caused and putting forward some teaching strategies so as to help underachievers out of their difficult position.