After investigation and analysis of tidal current and COD in Shijiu. Bay,the ADI method based on two-dimensional nondinear tidal wave equations is used to simulate the space-time distribution of the tidal current and matter concentration fields there after the 1st Shijiu Harbour work is finished.Then the probable space-time variation of tidal current and matter concentration caused by the 2nd to 4th harbour works are forecasted.The results show that the 2nd to 4th harbour works will greatly change the water dynamics of Rizhao Harbour, that with the extension of the mole and breakwater, the current direction along their respective two sides, and the tidal current speed,will be changed,and that eddies will occur around them. This will make the COD concentration increase rapiddly along the coast of Shijiu, and water quality will worsen and not be up to the 3rd class seawater quality standard of our country.