Abstract: There is a huge tidal sand system which is composed of the old sand body distributing in the coastal plain and the radial sand ridge distributing in south Huanghai Sea.Based on numerous drilling and geological ladar prospecting data,this paper emphatically studied the hydrodynamic environment and source of the old sand body by mains of magnetic fabric and heavy mineral analyses on the representative drilling cores.The results show that the old sand body was produced by tidal current in a hydrodynamic environment similar to the convergent-divergent tidal current field in south Huanghai Sea.The silt,which mainly came from the Changjiang River in the early and from the Huanghai River as well as the Changjiang River in the latter stage,was transported into the tidal current field by longshore current.So,the old sand body is a result of the middle-late Holocene continental-oceanic interaction.