Seafloor topography has always been the key of scientific study. Based on 1000 km2
high-resolution 3D seismic data of Lingshui Sag in Qiongdongnan Basin, South China Sea, the GeoFrame platform, Surfer 3D mapping, and other technologies were applied to characterize the current submarine landform of Lingshui Sag. Results show that the lower slope of Qiongdongnan Basin presented mainly three types of geomorphic units: channels (including large channel C1 and gully-lobe complexes G1-G3), cyclic steps, and submarine landslides. The width-depth ratio of channel C1 that was mainly scoured by debris transported via continental slope channels, is between 31.5 and 232. At the ends of G1-G3 of gully-lobe complex developed obvious lobes. The cyclic steps could be identified in the channel and submarine landslides. Squeeze ridges and underwater tongues were developed widely in the main body and the toes of slumps on continental slope. We speculate that the seafloor topography in the Lingshui Sag was mainly caused by submarine landsliding on the upper continental slope, which was intensified by deposit overload and sea level fluctuation, and finally the modern landform was formed.