Gas hydrate samples were first obtained in the Dongsha area, South China Sea (GMGS2) in 2013. High-resolution 3D seismic data in the area show various small landslide bodies developed as huge mass transport deposits. These bodies are divided into seven types on the basis of their shapes, internal structures and geneses (slide, collapse and deformation above BSRs, as well as the slump wedge, lens, block and sheet below BSRs). Based on this classification, detailed studies were conducted, including measurements of the slump body sizes and slope gradients of landslides, depiction of their three-dimensional characteristics, and research on the landslide distribution. To determine the genetic differences of these seven types, this study analyses the possibility of vertical flow-pattern-transformation and mechanisms of submarine landslide formation. Results show that the dominant factor influencing the submarine landslides in the Dongsha area is the free gas emitted from gas hydrate decomposition, with possible transformation between flow patterns. Finally, there are two kinds of relationships between submarine landslides and BSRs since the free gas either influences the submarine landslide bodies below or above BSRs, resulting in two types of submarine landslide body associations: Type A is characterized by submarine slide above BSRs and slump lens below BSRs, whereas Type B shows deformation above BSRs and slump blocks below BSRs. Type A is favourable for gas exploration because it indicates less decomposition and better sealing of gas hydrate layers.