This study identifies four phases (MTC 1, MTC 2, MTC 3, and MTC 4) of mass transport complexes (MTCs) on the northeastern continental slope of the Qiongdongnan Basin, through detailed interpretation of high-resolution 3D seismic data from the deep-water area of the basin, and amplitude-time slice analysis based on 3D seismic data. Among these, MTC 1, MTC 2, and MTC 4 are small in scale with low internal compression, whereas MTC 3 is the largest and exhibits the most intense internal deformation. By identifying and analyzing the kinematic indicators both within and outside MTC 3, the transport direction was determined to be southwest. The development of MTC 3 was divided into three stages: initial slope instability, sliding, and fluid conversion. Based on the identified morphologies and internal structural characteristics of the MTCs, and considering the tectonic and climatic evolution of the study area, it is suggested that the development of these MTCs was primarily controlled by a combination of factors, including slope gradient, polygonal fault activity, sea level fluctuations, and high sedimentation rates: the numerous continuously active faults developed in the lower part of the MTCs since the Late Miocene have acted as triggers for the formation of the MTCs; after the rapid sea-level drop and rise during the Late Miocene (10.5 Ma), changes in sediment strength and stratigraphic pressure parameters further promoted the development of the MTCs: since 5.5 Ma, rapid subsidence in the Qiongdongnan Basin has increased accommodation space, sediment influx, and slope steepening, thus providing favorable conditions for the formation of MTCs. The findings of this study contribute to the understanding of the sedimentary characteristics and triggering factors of pre-Quaternary MTCs on the northeastern continental slope of the Qiongdongnan Basin, and provide a reference for investigating the development of MTCs in the South China Sea region.