Using two-dimensional shallow-water tidal wave motion equation and continuity equation,combining with measured data of one tide station and four flow sites to verify the trend of points, obtained the realistic flow field, on which basis, the analysis that contain flow field, deposition and the water quality caused by the project could be obtained. The results show that: the southwest region produces the velocity increase,while the other regions of it and the area near the pier produce the velocity decrease. The maximum reducing of depth happens in deposition equilibrium up to 1.2 m; the increases of erosion change with the amount of decreasing distance from the dike erosion and scour, while the equilibrium volume of it is 0.1 ~ 0.3m. COD discharging in normal circumstances has little impact on the surrounding water; and when it happens in the accident, its influential sphere expands, but the impact on the surrounding water quality is still very small.