Literature review is a style different from research papers, which is composed of understanding, sorting, comprehensive analysis and evaluation after researchers read the literature on a certain topic in advance. The purpose of the review is to reflect the new level, new trends, new technologies and new discoveries of a certain discipline. From its history to present situation, existing problems and development trend, we should make a comprehensive introduction and comment. On this basis, I put forward my own opinions, predict the development trend of technology, and lay a good foundation for topic selection and opening.