Abstract: Some formations of Ordovician were established based on fossil assemblages rather than lithology. According to the principles of the multiple stratigraphic division, the authors in this study contend that the Xainza Formation should be abolished, and the basal boundary of the Dewukaxia Formation should be redefined. Finally the stratigraphic ages and correlation of the Ordovician lithostratigraphic units in the study area are discussed.