Submarine landslides are among the most common and destructive geological hazards on continental margins. Their development can significantly reshape seafloor morphology, generate high-density turbidity currents, and even trigger catastrophic tsunamis, posing serious threats to the safety and operation of sub-sea engineering infrastructures. The formation of submarine landslides typically involves long-term geological processes influenced by multiple interacting factors. Some large-scale submarine landslides exhibit multi-stage sliding events with complex movement histories. However, current understanding of the developmental characteristics and formation mechanisms of multi-phase submarine landslides remains limited, which hinders scientific insight into their evolutionary patterns. Based on high-resolution, two-dimensional (2D) multichannel seismic and borehole data, six phases of Mass Transport Deposits (MTDs) resulting from submarine landslides have been identified in the Kaiping Sag on the northwestern continental margin of the South China Sea. According to the established regional sequence stratigraphic framework, these MTDs are mainly concentrated within the Lower Hanjiang Formation and Yuehai Formation. Seismic interpretation results indicate that the internal structure of MTD 1 and 2 is highly deformed and significantly altered by subsequent geological processes, whereas MTD 3 to MTD 6 exhibit typical landslide features such as prominent headwall scarps and lateral margins. Calculation of sedimentation rates during the occurrence of each phase of MTDs reveals that high sedimentation rates occurring during periods of low sea level provided the necessary sediments for the occurrence of landslides. This rapid sediment accumulation likely prevented the timely expulsion of pore fluids, leading to elevated pore pressure within the sediments and the formation of unstable weak layers. In addition, the widespread development of tectonic normal faults (e.g., Shenkai Fault) and their intersecting relationships with all six MTDs strongly suggest that fault activity also played a significant role in triggering these landslides. This study provides new insights into the formation mechanisms of submarine landslides along the northwestern continental margin of the South China Sea, offering important scientific support for hydrocarbon exploration, geological hazard risk assessment, and disaster prevention and mitigation in the region.