Abstract: The Pearl River Mouth Basin is an important oil and gas producing area in the South China Sea, of which the AD 15 Sag is an important hydrocarbon-rich sag. However, due to limited understanding on the complexity of the oil and gas reservoirs, significant exploration progress has not been made in the AD 15 Sag. Based on the evaluation concept of "source, sink, accumulation", we conducted in-depth and systematic research on the oil and gas migration and accumulation in the northern gentle slope zone of AD 15 Sag using 3D seismic data, and combined them with logging and geochemical data. Result show that the differential evolution of boundary faults controlled the formation of the AD 15 Sag, and strong fault activity during the peak period of the depression promoted the formation of a "contiguous lake basin" in the areas to the south of the sag, with a large subsidence rate and a wide and deep lake basin. The middle-deep lake high-quality source rock with great potential for large-scale hydrocarbon generation during the 4th and 3rd members of the Wenchang Formation. The inherited fluid migration structural ridge controls the main migration and accumulation direction of oil and gas, and the coupling of longitudinal differential dredging of early and late faults and lateral sand bodies formed a series of three-dimensional transport of oil and gas. Under the control of regional caprocks, oil and gas efficiently converged in high porosity and permeability reservoirs along structural ridges, forming a fault-cap-ridge joint control model for long-distance oil and gas migration and accumulation in gentle slope zone of the AD 15 Sag. Therefore, this study provided a guidance and reference for further deepening oil and gas exploration and achieving new breakthroughs in the research area.