In order to clarify the controlling factors of organic matter enrichment in fine- grained sedimentary rocks in the Lower Permian Zhanjin Formation in the central Qiangtang Basin.Methods:Forty fine- grained sedimentary rock samples were presented in this study to analyse the micropetrological characteristics, organic carbon content, elemental geochemistry, and mineralogy, and then explore the evolution of paleoenvironment and its control on organic matter enrichment.Results: The results indicate that the fine- grained sedimentary rocks can be classified into five lithofacies types based on their chemical composition, grain size and sedimentary structures, include the massive siliceous mudstone, massive siliceous silty mudstone, massive siliceous siltstone, laminated siliceous mudstone and laminated siliceous siltstone. However, the variation in organic carbon content is minimally influenced by its lithofacies changes. The patterns of geochemical indicators and variation of framboidal pyrite size suggest that above fine- grained sedimentary rocks were deposited in an oxic to dysoxic environment associated with significant influx of iron- rich and magnesium- rich terrigenous detritus, and minor hydrothermal activity. The influx of detrital nutrients not only promoted biological flourishing and increased the paleoproductivity levels of surface waters, but also enhanced the adsorption capacity for organic matter.Conclusions: This study concludes that the organic matter enrichment in these fine- grained sedimentary rocks is primarily controlled by paleoproductivity, clay mineral adsorption, and rapid sedimentation rates, the influence of redox conditions can be neglected.