Abstract: Based on the three-dimensional numerical model, this article simulates the distribution of the DIN concentration in Liaodong bay and investigates the influence of the variation of Liao river discharge on the distribution of DIN concentration, by coupling the hydrodynamic module and the water quality module of the model.The simulation results show that the DIN is accumulated during autumn and winter while consumed during spring and summer and the concentration of DIN gradually declines from the northeast to the southwest.In the northwest of Liaodong bay, high concentration of DIN exits in the Liao River estuary and the Daliao river estuary.With the concentration of the DIN input from the river remaining the same, strong hydrodynamic condition of Liao river will increase the concentration of DIN in the whole Liaodong bay, causing more serious water pollution.A weak hydrodynamic condition will improve the water quality of the sea area to some extent.