The classification of thymoma has always been controversial topil in recent years. It hasn’t been unified because of the morphological diversity of thymoma, the heterogeneity of tumour cells and the lack of simple and effective observation index. With the development of diagnostic technique and oncobiology research, several classification methods have been drawn off, including its World Health Organization(WHO) lassification. We reviewed the main classification and discussed the problems of each classification method and their clinical guiding significamce, summarized the development tendency, methods assist the classification and clinical research of thymoma.