A 3D,time-dependent,baroclinic,hydrodynamic and salinity model was implemented and applied to the Oujiang River estuarine system in the East China Sea.The model was driven by the forcing of tidal elevations along the open boundaries and freshwater inflows from the Oujiang River.The bottom friction coefficient and vertical eddy viscosity were adjusted to complete model calibration and verification in simulations.It is demonstrated that the model is capable of reproducing observed temporal variability in the water surface elevation and longitudinal velocity,presenting skill coefficient higher than 0.82.This model was then used to investigate the influence of freshwater discharge on residual current and salinity intrusion under different freshwater inflow conditions in the Oujiang River estuary.The model results reveal that the river channel presents a two-layer structure with flood currents near the bottom and ebb currents at the top layer in the region of seawater influenced on north shore under high river flow condition.The river discharge is a major factor affecting the salinity stratification in the estuarine system.The water exchange is mainly driven by the tidal forcing at the estuary mouth,except under high river flow conditions when the freshwater extends its influence from the river’s head to its mouth. A 3D, time-dependent, baroclinic, hydrodynamic and salinity model was implemented and applied to the Oujiang River estuarine system in the East China Sea. The model was driven by the forcing of tidal elevations along the open boundaries and freshwater inflows from the Oujiang River The bottom friction coefficient and vertical eddy viscosity were adjusted to complete model calibration and verification in simulations. It is characterized that the model is capable of reproducing observed temporal variability in the water surface elevation and longitudinal velocity, presenting skill coefficient higher than 0.82. model was then used to investigate the influence of freshwater discharge on residual current and salinity intrusion under different freshwater inflow conditions in the Oujiang River estuary. the model results reveal that the river channel presents a two-layer structure with flood currents near the bottom and ebb currents at the top layer in the region of seawater influenced on north sh ore under high river flow condition. the river discharge is a major factor affecting the salinity stratification in the estuarine system. the water exchange is mainly driven by the tidal forcing at the estuary mouth, except under high river flow conditions when the freshwater extends its influence from the river’s head to its mouth.