The accumulation mechanismof lithologic reservoir in tight sandstone gradually becomes the main difficulties and frontier areas for exploration arrangement in Yanchang Formation ofOrdos Basin. Based on the analysis of potential source rock and oil-to-source correlation, combined with pressure field evolution, fluid dynamics and fluid kinematics, the accumulation mechanism of lithologic reservoir of Chang 8 member is discussed by using petrology and advanced techniques used in geochemistry and basin numerical simulation. The results show that the hydrocarbon of Chang 8 member mainly originated fromthe generating organic matter in Chang 7 and Chang 8 member ofYanchang Formation. Reservoirs of Chang 8 member take on two-stage charging processes, and the main charging time is in late Early Cretaceous (105～95 Ma). Since 210 Ma, the pressure field evaluation experienced three processes: early increase, middle quick increase and late reduce. Moreover, the broad hydrocarbon generation in Early Cretaceous and the tectonic compression inMiddle-Late Yanshanian are the main formation mechanismfor overpressure. The accumulation model of lithologic reservoir in Chang 8 member presents near-source charging, latent conduit and rapid accumulation.