Based on seismic and bathymetric data, the authors focused in this paper on the deep water topography of the Qiongdongnan Basin and the control of topography over the deepwater sedimentation. The results show that the submarine topography of the Qiongdongnan Basin can be divided into three units of the continental shelf, the continental slope and the deep-sea plain. The results prove that the types of sedimentary facies are closely related to the gradient of the slope. The gradient not only controls the distribution of types of gravity flow deposits, but also the adjustment of slope system.