Dendritic canyon system is the most widely distributed type of submarine canyon on the global continental margin. It is important in understanding the field of deep- water sedimentation and marine geological disasters. Based on high resolution multi- beam sounding and two- dimensional seismic profile data, taking the Xisha sea area of the South China Sea as the study area, the dendritic canyon system in the north of Dongdao is studied. The Dongdaobei submarine canyon is distributed in the range of 1000 ~ 3150 m water depth, which is generally composed of one main canyon and four branch canyons. The sediment supply at the upstream of the canyon comes from the northwest of Dongdao (area I) and the east of the Yongxing Plateau (area II). Sediments from zone III in the northeast of Dongdao are injected into the middle reaches of the canyon. Sediments are transported to deep water through canyon system and mass- transport deposits system. A large number of submarine pockmarks are distributed around the north slope of the main canyon. The side wall of the canyon collapsed backward in a ladder shape. Sediment waves are developed on the south slope of the main Canyon, which are affected and transformed by tides and waves. The main canyon with overall SW- NE strike is controlled by the strike of the main fault, while seamounts are distributed on the south bank of the canyon, controlling the turning of each section of the main canyon. At the same time, the faults developed in the lower stratum of the canyon and its periphery control the side wall of the canyon to descend in a ladder shape to the valley bottom.