【Abstract】This study introduces the research background firstly， and then the definition and classification of learning strategies are mainly presented， which provides a review of learning strategies.
　　【Key words】 learning strategies； definition； classification
　　I. Background
　　For a long time， teaching methods were the center of foreign language teaching research. By the 1970s， the focus of foreign language teaching research had changed greatly， from teachers how to teach to students how to learn. What’s more， learning strategies originated in the middle of the 1970s. From then on， the study of learning strategies for learners centered has been an important research area in second language （L2） acquisition and foreign language teaching research.
　　II. Definition of learning strategies
　　The word “strategy” comes from Greek， which means “the art of general”. That is to say， strategies are used by different people which can be explained as stratagems， plans and policies and then skills， strategies， processes and approaches. In that case， there is no a specific definition for learning strategies because different researchers hold diverse views towards it， as shown in table1.
　　Based on the above opinions， learning strategies are described in a variety of forms， but they are similar in many ways. This study believes that learning strategies are the specific measures， methods， skills and other behaviors that learners adopt to acquire knowledge， promote learning and increase learning efficiency.
　　III. Classification of Learning Strategies
　　After a general understanding of the concept of learning strategies， many researchers classify learning strategies according to different standards and the typical categories are as follows：
　　Oxford （1990） proposes two categories. One is direct strategies， which include memory， cognitive and compensation strategies. The other one is indirect strategies， which include meta-cognitive， affective and social strategies. In the same year， O’ Malley and Chamot put forward three major categories： meta-cognitive， cognitive and social or affective strategies. In the meantime，， each branch is classified in detail.
　　The above classifications of learning strategies have their similarities and they lay a solid foundation for the study of learning strategies in L2 acquisition. Consequently， it is necessary to study the classification of learning strategies for learners to master strategies.