Abstract: Multiple inter-salt layers composed of organic-rich fine-grained sedimentary rocks are developed in the Qianjiang Formation, which is a potential target for shale oil exploration in Qianjiang sag. However, the unclear understanding of the mechanism of organic matter enrichment in salt lakes restricts the study of shale oil accumulation mechanism. The geological data including core, thin section, X-ray analysis and major, trace, rare earth elements were integrated to study the enrichment mechanism of organic matter in the inter-salt stratum of the 10th rhythmite of the Lower Member 3 of Qianjiang Formation. According to the mineral composition and lithofacies types, the inter-salt stratum of the 10th rhythmite of the Lower Member 3 of Qianjiang Formation can be divided into three sections. The upper and lower sections are composed of bedded dolomitic mudstone and glauberite, with average TOC content of 0.83%, while the middle section is composed of laminated marlstone and laminated dolomitic mudstone, with an average TOC content of 1.35%. The crystal morphology of pyrite and geochemical characteristics of elements indicates that inter-salt layers in the Qianjiang sag has recorded hydrothermal activity. During the sedimentary period of the middle section of inter-salt layers, the climate was relatively humid, with a strong reducing condition, low salinity and high biological productivity. The upper and lower sections of inter-salt layers were formed in a dry and hot climate, with a weak reducing condition, high salinity and low biological productivity. This study indicates that the enrichment of organic matter in inter-salt layers of Qianjiang sag was resulted from the hydrothermal activity and climate change. The hydrothermal activity played an important role in improving the biological productivity in salt lakes, which brought nutrients to the surface waters.The dry-wet changes of paleoclimate can affect the preservation of sedimentary organic matter by controlling the changes of redox and salinity of the salt lake.