On account of the special natural characteristics of Qiantang estuary,the regulation and reclamation in large scale on Qiantang estuary have been carried out since 1960’s.Based on the numerical simulation of the hydrodynamics and water environment in Hangzhou bay by MIKE,the influence on flow field,salinity field and water quality of Hangzhou bay has been studied.The result shows that the project affects only its adjoining waters,and it increases the speed of water flow in the estuary.The project can also make the salinity contour backward,and decrease the intensity of saltwater intrusion.The contamination from the Qiantang river will diffuse faster after the reclamation project,while it will reduce the water pollution in Qiantang estuary.