Abstract:Compare of the different periods of Zhanjiang Bay bathymetric chart,In recent years,The sandbars of two sides of Zhanjiang Bay channel are shrinking.sandbar topography are evolving gradually from hills to comb topography.The Isobath of south channel is approaching to the coastline of DongHai Island. The coastline is eroding seriously. We make a comprehensive analysis of the causes in article, The results show that, in recent years, there are many large-scale reclamation projects in Zhanjiang Bay,Which Changed the tidal volume,Sediment sources,Suspended sediment concentration and Flow characteristics .Making the sandbar of outside the Bay in equilibrium occurs erosion and deposition.