The petromineralogy, organic geochemical, and reservoir pore space characteristics of 15 lacustrine shale samples from the Qingshankou Formation in the Songliao basin were studied. The experimental methods of XRD, pyrolysis, stepwise pyrolysis, stepwise extraction and stepwise NMR testing were comprehensively applied to characterize the content, composition and distribution characteristics of shale oil in different occurrence states of the Qingshankou Formation. The evaluation of retained hydrocarbon content, production potential, exploration constraints factors and suggestions are further discussed. The following conclusions can be obtained from this study: ① The mineral composition of the Qingshankou Formation is relatively homogeneous, mainly shale with high clay content, and the clay mineral characteristics dominated by illite are favorable for reservoir fracturing. The rich distribution of organic matter is relatively uniform, and the average TOC is 2. 41%. It has good petroleum bearing property with light oil quality, high saturated hydrocarbon content and oil saturation index. ② The occurrence state of shale oil is defined as free oil, free- adsorbed oil and adsorbed oil extracted from different particle sizes under the conditions of cold extraction and Soxhlet extraction. The free oil is mainly composed of light components, while the heavy components are higher in the adsorbed oil. The larger pores are mainly composed of free oil, and most of the adsorbed oil is distributed in the smaller pores. The change in chemical composition of free oil and adsorbed oil also reveals the component fractionation effect in the process of oil micro- migration. The oil after oil discharge and migration has higher saturated hydrocarbon+aromatic hydrocarbon content, smaller molecular weight and lower Pr/n- C17 and Ph/n- C18 values, indicating greater flow possibility. ③ The oil quality of the Qingshankou Formation is relatively superior, but the relatively high clay mineral content is the restrictive factor that needs to be paid attention to in production. The micro- migration of shale oil indicates a greater possibility of production. In the exploration process of this area in future, we can try to find oil migration and accumulation areas.