Saline shales are widely developed in the Mesozoic and Cenozoic continental saline lacustrine rift basins in China, containing abundant shale oil resources. The development of sweet spots in shale oil plays is closely related to the organic matter richness, but the key factors controlling differential enrichment of organic matter in saline shales are still unclear few and controversial. Taking the Dongpu Depression in the Bohai Bay Basin as an example, this study conducted the TOC, FE-SEM, energy spectrum, major, trace, and rare earth elements analyses on the Es3 (Third member of the Paleogene Shahejie Fm) Shales, exploring the correlations among the organic matter richness with paleoclimate, paleo-salinity, sedimentation rate, paleo-productivity, and redox condition. Results show that the organic matter enrichment degree is jointly controlled by paleo-productivity, paleo-salinity and sedimentation rate. The greater the paleo-productivity is, the greater the organic matter enrichment degree is. With the increasing paleo-salinity and sedimentation rate, the organic matter enrichment degree increases first and then decreases. Redox conditions have little effect on the enrichment of organic matter, which is mainly related to the generally strong reduction condition of the shale cores. The combination of high paleo-productivity, proper paleo-salinity and proper sedimentation rate is most favorable for the organic matter enrichment. Differential enrichment of organic matter within shales is one of the important contents for Unconventional Petroleum Sedimentology studies. Revealing the key factors controlling differential enrichment of organic matter is of great significance to the exploration and development of lacustrine shale oil in China.