Literature review is a scientific paper in which the author comments on the historical background, previous work, focus of debate, research status and development prospect of a certain issue. A review is a research report that evaluates a certain topic or technology on the basis of a review. Literature review of extended materials refers to the comprehensive arrangement, analysis and comment of related documents in order to discuss and study a special topic. It also refers to an oral or written summary report on this point. The first important step after determining the subject in scientific research. The purpose is to understand the main work and existing problems of others on this subject, so as to absorb the achievements, experiences and lessons of predecessors and make research plans. Literature review is an academic paper that collects a large amount of relevant information about the topics, problems or research topics in a certain field, a certain specialty or a certain aspect, and then comprehensively introduces and expounds them through reading, analyzing, refining and sorting out the latest progress, academic viewpoints or suggestions of the current topics, problems or research topics.