Abstract: The northern slope of the Lingshui Sag in the Qiongdongnan Basin develops a series of NWW-SEE trending strike-slip faults. However, previous studies have lacked systematic characterization of these structures; and their role in hydrocarbon accumulation in the middle-shallow layers remains unclear, hindering exploration progress in the shallow sequences. Based on high-resolution 3D seismic data, we conducted detailed structural interpretation to systematically analyze the geometric and kinematic characteristics of the southern strike-slip fault zone, with a focus on its control mechanism on hydrocarbon accumulation in the middle-shallow layers (Pliocene Yinggehai Formation-Holocene Ledong Formation). Results indicate that the southern strike-slip fault zone exhibits a dextral left-stepping en-echelon distribution, characterized by typical transtensional features and negative flower structures as shown in cross-section. Integrated with regional tectonic evolution analysis, its main active period was determined as the Ledong Formation depositional stage (approximately 1.8 Ma). This study is the first to systematically propose that the strike-slip fault system exerts four key controls on middle-shallow hydrocarbon accumulation: ① It served as the main vertical migration pathway, connecting deep-source rocks of the Yacheng-Lingshui formations, with geochemical evidence confirming its role as the core channel for upward hydrocarbon migration; ② It controlled the development of various trap types, including fault blocks, fault noses, and en-echelon anticlines on the descending side, while promoting the formation of lithologic traps by tilting; ③ Associated structural fractures effectively improved the physical properties of fine-grained reservoirs, forming fractured mudstone gas reservoirs; ④ Quantitative evaluation showed that, although the faults extend to shallow depths, thick regional mudstone caprocks and high normal stress on fault surfaces jointly provided effective sealing, ensuring favorable preservation conditions. Therefore, the southern strike-slip fault zone is a key geological factor controlling hydrocarbon migration and accumulation in the middle-shallow layers of the northern slope of the Lingshui Sag. The overlapping segments of the fault zone integrated efficient migration, reservoir improvement, multiple trap types, and good preservation conditions, representing the most favorable targets for future hydrocarbon exploration. This study enhanced the understanding of strike-slip fault control on hydrocarbon accumulation in the Qiongdongnan Basin and provided theoretical guidance for exploration in the middle-shallow layers of the study area.