Abstract: The pools of sand lens in the third section of Shahejie Formation in Niuzhuang sub-depression were analyzed. The results showed that reservoir-forming mechanism of lithological pools included subtle passage and episodic replacement. Oil and gas migrated from source rock to sands, and formation water and the early filled hydrocarbon blew out of sands by subtle passage system. The hydrocarbon of numerous litholocgical pools was episodically gathered in faults, and large and medium size tectonic pools were formed in mid-shallow layers. Oil and gas was annularly distributed outside the basin in the early stage and inside the basin in the late stage. The lithological traps were the minimum oil-gas gathering and transferring stations in the course of hydrocarbon migration and accumulation.