Semi- deep to deep lacustrine shale strata within the first member of the Cretaceous Qingshankou Formation (K2qn1) in the southern Qijia sag of the Songliao basin are well- developed and represent a typical target for tight shale oil exploration. Using data from drilling, logging, and core tests, we conducted a comprehensive study of the geological characteristics, lithofacies type, and tight shale oil enrichment model of the K2qn1 using the SYY1 well as an example. Our results indicate the K2qn1 shale exhibits three kinds of sedimentary structures: Bedded, massive, and laminated. Based on total organic matter (TOC) content, sedimentary structure, and mineral composition, the K2qn1 shale in the SYY1 well can be divided into five lithofacies: Bedded siliceous mudstone with high TOC (＞2. 0%), massive siliceous mudstone with high TOC, bedded siliceous mudstone with moderate TOC (1. 0%~2. 0%), massive siliceous mudstone with moderate TOC, and laminated siliceous mudstone with moderate TOC. Among these, the bedded siliceous mudstone lithofacies with high TOC is the main lithofacies and the most favorable to control the enrichment of shale oil. It boasts high organic matter content (TOC values generally ranging from 2% to 3. 5%), good free oil content (S1 values up to 19.4 mg/g), and abundant movable hydrocarbons (average OSI values exceeding 300 mg/g). Its reservoir space is mainly mesoporous, with a proportion of macropores also developed. Compared to other lithofacies, it exhibits a relatively continuous pore size distribution, dominated by slit pores, and good connectivity. The K2qn1 shale in the SYY1 well displays a high thermal evolution degree (average Ro value of 1. 26%), indicating significant hydrocarbon generation from organic matter. In the bedded siliceous mudstone lithofacies with high TOC, light components constitute 50% to 55% of the shale oil, implying good oil mobility. In addition, this lithofacies is characterized by well- developed, dense bedding fractures. These fractures connect micro- nano pores, forming a pore- fracture network system that significantly enhances reservoir performance and rock permeability. Therefore, the bedded siliceous mudstone lithofacies with high TOC, developed in the semi- deep to deep lacustrine facies of the southern Qijia sag, presents a promising target for shale oil exploration. This lithofacies exhibits favorable material conditions and effective reservoir space for shale oil enrichment, while the surrounding tight massive shale acts as an effective seal, ensuring excellent preservation conditions.