Abstract: To understand the grain size characteristics and distribution of surface sediments over the cape-baycoast,Wujiao Bay of Dongshan sea area were taken as a typical area for the study.Surface sediment samples were collected from 5 profiles pependicular to the Wujiao Bay coastline,each of them were taken from 0 to 5 cm.Grain sizes of the surface sediments were analyzed by Mastersizer 2000 laser particle size analyzer.Sampling position and profile altitude were measured by GPS.Results showed that,sandy sediments(16~500 μm)were the primary particles in the study area,and sand-sorting was much better,which agreed with the sediment characteristics of Southern China.Grain size distribution trended to be smaller northwards in Wujiao Bay,which resulted from the capebay coast geomorphology and the dynamic effect of wind wave.Peak value of grain size distribution curves along the profile increased from nearshore waters to the middle tidal zone while decreased to the low tidal zone,caused by the offshore hydrodynamic environment and coastal landform.In general the comprehensive effects,such as the cape-bay geomorphology,wind-wave,tidal effect,and local sediment provenance,contribute to the characteristics ofgrain size distribution in Wujiao Bay.