Abstract: North Haizhong Sub-sag, is located in the junction zone between Weixi'nan Sag and Haizhong Sag, Beibuwan Basin, where the Cenozoic fault system is extremely complex. To clarify the controlling effect of such intricate fault architectures on hydrocarbon accumulation, this study systematically analyzes the distribution, evolution, and reservoir-controlling effects of the fault system based on seismic interpretation, fault geometry and kinematics, and hydrocarbon shows. The results indicate that three sets of extensional faults are mainly developed in the study area, trending nearly EW, NEE, and NWW, which can be classified into four subsystems: Type I (long-term inherited), Type II (segmented growth), Type III (early extensional), and Type IV (adjustment). The development and evolution of the fault system exhibit temporal cyclicity over time, showing alternating weak-strong-weak phases. Hydrocarbon accumulation is multi-dimensionally controlled by the fault system: effective source-connected faults act as pathways for hydrocarbon migration, and provide ample hydrocarbon supply to surrounding favorable structures; the "fault-ridge-sand" ternary coupling forms an efficient three-dimensional migration framework, significantly enhancing hydrocarbon migration efficiency; reverse-blocking traps exhibit superior lateral sealing capacity, providing essential conditions for large-scale hydrocarbon accumulation. This research reveals the controlling mechanism of the fault system on Paleogene hydrocarbon accumulation in North Haizhong Sub-sag, providing a reliable reference for hydrocarbon exploration in adjacent areas and other complex rift basins with similar geological settings.