With the Hejiakouzi stratigraphic section of Qingshuiying Formation in the northern Ningnan basin chosen as the research target, this study carried out research of the lithology of Qingshuiying Formation, major element features of gypsum, and organic geochemical parameters of mudstone. The results show that lithology of Qingshuiying Formation is dominated by intercalated graygreen and purple mudstone and gypsum. The Qingshuiying Formation can be divided into eight secondary depositional cycles and three primary cycles. CaO content of gypsum reflects chemical deposition of gypsum in saline lake basin, with Al2O3from terrigenous clastic sedimentation. The lower segment of the Qingshuiyin Formation is gypsum deposited in deep water of saline lake and the gypsum in middle segment was deposited in shallow water; mudstone in the lower part of the Qingshuiyin Formation contains high TOC and hydrocarbon potential (S1+S2), indicating that climate was relatively humid and water was deep at early stage of saline lake evolution. Besides the decreasing degradation potential, organic matter was derived mainly from high plant sources, most of which were from land. The study shows that the Qingshuiying Formation in the Ningnan basin resulted from sedimentation of both evaporite and terrigenous clastic rock. But the evolution of saline lake did not reach the high evaporation stage at which halite (such as sylvine) can be precipitated. The Late Paleogene evolution of saline lake can be divided into early closed deep saline lake, middle closed shallow saline lake and late open shallow saline lake stages, and was good response to the continuing tectonic subsidence and the regional sedimentary event that all secondary sedimentary depressions developed into a unified lake.