Abstract: Based on the practically drilled geological data and the experimental test results of oil and gas reservoirs, combined with the theory of fluid compartment, this paper studies the hydrocarbon accumulation system of Pinghu Formation in K structure of Xihu Sag to improve the prediction accuracy of favorable zones. The results show that under the regional seal of the deep-water mudstone in the top of the middle section of Pinghu Formation, the broom-like contemporaneous fault system further divided the "mud-coated sand" stratigraphic system, forming secondary seal boxes controlled by the fault system of different levels and different active periods. The oil and gas of K structure were mainly sealed in pressure compartments, and the deep-water mudstone in the top of the middle section of Pinghu Formation controlled the vertical distribution of oil and gas. The result will provide importment guidance for the optimization of oil and gas exploration targets in K structure of Xihu Sag.