According to the analyses of element geochemistry, organic geochemistry and isotope geochemistry of mud-stone samples from the 4th member (Es~4) and the lower subsection of the 3rd member (Es~3) of the Shahejie Forma-tion in the Langgu Sag, combined with the characteristics of lake evolution and climate change, it was discussed in this paper the changes of salinity, redox condition and productivity as well as the enrichment mechanisms of organic matter. During the formation stage (Es~4), the lake was deposited in an inactive tectonic activity with arid climate, brackish water, stable water column stratification, water bottom anoxia and lower enrichment of organic matter. When the lake developed to the peak stage (the lower subsection of Es~3), the basin subsided strongly with hu-mid climate, fresh water and weak reducing environment in the bottom water. The productivity of surface water was high triggered by a great quantity of nutrients inflowed by direct runoff. The enrichment of organic matter in lacustrine sedimentation was controlled by the productivity and redox conditions during different lake evolution stages. In Es~4, the enrichment of organic matter was mainly controlled by the anoxic environment in the bottom water, while in the lower subsection of Es~3, it was closely related to the high productivity of surface water.