Abstract: A numerical model based on Delft 3D, an open source three-dimensional hydrodynamic model, was built to simulate the temporal and spatial distribution of tidal level, tidal current, temperature and salinity in Xiangshan bay. Calculated results were found to match the measured data closely, which demonstrated the model was able to simulate the hydrodynamic characteristics of Xiangshan bay accurately. Based on the validated flow model, a water quality model was built to investigate the migration and transformation process of pollutants in Xiangshan bay. The simulation results were again found to match with the measured data and the model is capable of reproducing the variation trend of the most water quality variables in Xiangshan bay. The verified water quality model was then applied to analyze the influence of the sewage outlets on the water quality variables in Xiangshan bay considering the timing of the discharge (during ebb tide), variation of discharge rate and layout of the sewage outlets. The simulation results showed that the water quality environment of Xiangshan bay was clearly affected by the locations of sewage outlets and the three design scenarios considered could all directly reduce the DIN concentration in the bay with different scenarios shown different influencing characteristics.