Abstract: For a total of 153 surface samples taken from the southern South China Sea, grain size analysis, grain size parameters calculation and Q-mode hierarchical cluster analysis have been carried out, and the grain size distribution pattern, sediment types and influencing factors discussed in this paper. Among the samples, silty sand, sandy silt, silt and mud dominate, and the distribution of sediments is approximately parallel to the isobath in a zonal pattern, with mud as a major. Supported by Q-mode hierarchical cluster analysis, the sediments of research area can be divided into two types, coarse sediments (sand and silt) on the outer continental shelf and shelf break, fine sediment (silt) on the continental slope. The boundary of the two occurs along the isobath of 500 meters. Together with the data of grain size, it is deduced that the two types of sediment are from different origin, one is related to the mixing of the modern sediment and the relict sediment on the outer continental shelf and continental shelf break region, the other is the modern sediment on the continental shelf alone. The grain size distribution of surface sediments in the southern South China Sea is mainly dependant on provenance, hydrodynamic condition, water depth, geomorphology and current system.