Based on the bathymetric and topographic data of five years from 1960 to 2021 in the Dayushan Sea area of Zhoushan，we discuss the influence of the Dayushan reclamation project on the changes of surrounding seabed erosion and siltation.We adopt the digital quantitative erosion and siltation calculation and the method of characteristic isobath superposition based on GIS technology to study the changes in surface erosion and siltation and surface morphology of typical underwater terrains near the project.The results show that the whole study area is in a slight erosion state in natural conditions.After reclamation，the south trough silts near shore，while the outer and northern deep troughs continue to erode，and the shoals on the east and west show significant siltation.The Dayushan reclamation project has greatly changed the original shoreline distribution and the surrounding hydrodynamic sediment environment.This eventually leads to sea-bed erosion and siltation changes near the reclamation area，but the seabed tidal flat distribution is unchanged.