Yangshan deepwater port is the first offshore island port in China,built in the Northern Island chain made up mostly the small Yangshan island,the Southern Island chain made up mostly big Yangshan island is across the water.Two island chains form a funnel shaped area facing west towards Hangzhou Bay which carries the very high suspended sediment concentration.In order to get enough docklands and straight shore line works,the project blocked the three branch channels of the North Island chain and connected the inlets,substantially changed the natural environment.Based on the special environment,according to mass of hydrological and bathymetric data accompanying with the works,and the changes in circulating current caused by tide and main channel flow field structure,this article stated the impact of water and suspended sediment movement during different works period,and suggested that adjusting the first Yangshan deepwater port construction plan,keeping Kezhushan branch is a scientific and rational choice.