During the Cretaceous period, the Qingshankou Formation in the Songliao basin deposited thick layers of lacustrine shale rich in shale oil resources. However, the spatial distribution of organic matter abundance in these shales is highly heterogeneous. Therefore, determining the main factors controlling organic matter enrichment in different depositional environments is crucial for shale oil exploration in the Songliao basin. This paper systematically analyzes organic matter abundance, rock pyrolysis parameters, mineral composition, major elements, and trace rare earth elements in shales from various lacustrine environments (shallow, semi- deep, and deep) in the Qing 1 section of the southern Songliao basin. Through quantitative analysis, we establish a model for organic matter enrichment specific to each environment. Our results indicate that a combination of low to moderate detrital input, a salinity gradient in brackish water, and reducing conditions are conducive to organic matter enrichment. Shallow lake environments, characterized by freshwater and fluctuating weakly oxic to weakly reducing conditions, exhibit high primary productivity. However, poor preservation conditions limit overall organic matter enrichment, resulting in a “productivity- driven” model. Semi- deep lakes, predominantly reducing with localized weak oxidation and brackish water, demonstrate significant control of organic matter enrichment by both preservation conditions (correlation coefficient=0. 65) and nutrient availability (correlation coefficient=0. 45), supporting a “productivity- preservation co- control” model. Deep lake environments are dominated by anoxic and reducing conditions, characterized by salinity stratification and brackish to saline water. Anoxic conditions are the main reason for organic matter enrichment in these settings, adhering to a “preservation model.” The restricted nature of deep lake environments leads to nutrient- starved basins, resulting in low primary productivity and limiting organic matter accumulation (correlation coefficient=0. 8). This paper reveals the key role of brackish water reducing environments and salinity stratification in controlling organic matter enrichment within the Qingshankou Formation. By establishing distinct organic matter enrichment models for each lacustrine environment, this research provides valuable insights for guiding future shale oil and gas exploration and development strategies within the Songliao basin.