Abstract: On the basis of the theory of modern stratigraphy, the Xiashan Group in Jiangxi may be divided into four formations. The connotations of the original Yunshan, Zhongpeng and Sanmentan Formation have been redefined and a new formation-the Zhangdong Formation-have been separated from them. This paper expounds the diachronism of various formations from west to east on the basis of fossils and rock characters and through correlation made by lateral extension.