Clay mineralogy and geochemistry of detrital sediment samples collected in a core of the Mengyejing Potash salt mining of Simao basin, Yunnan were used to evaluate the provenance and sedimentary environment evolution of paleolake. The clay mineral assemblages, La/Th Hf, La/Sc Th/Co, La Th Sc diagrams and values of Cr/Th, Al2O3/TiO2 indicate that the provenance of the detrital sediment is mainly granodiorites. And the major element results indicate that the formation of clay minerals is accompanied by leaching of Ca and Na first and enrichment of K and Mg. Fe and Mn, is deplete because of the limitations provenance. Combined with the formation conditions of clay minerals, we suggest that the paleolake experienced a variable paleoclimate evolution process which characterized by warm and wet to warm and dry (the stage of salt forming and sylvite forming) to warm and wet (the desalination stage). The hypersaline environment and burial diagenesis affected the clay mineral assemblages significantly, documented by the widespread occurrence of illitization and chloritization in core samples. Thus, the clay mineral assemblages of illite+chlorite, combined with the abundance of Mg rich chlorite and the abnormally high value of MgO of detrital sediments at the corresponding stage are indictive of the evolution of salt forming and sylvite forming stage.