Based on SEAWAT, a 3D seawater intrusion numerical model was established to simulate the unstable seawater intrusion process in the coastal aquifer of the Dagu River Basin near Jiaozhou Bay. The observation data of groundwater level and Cl－ mass concentration from January 1,2010 to June 1,2018 was used to calibrate and validate the hydrogeological parameters of the seawater intrusion numerical model. At the same time, the global sensitivity analysis was used to evaluate the impact of hydrogeological parameters such as aquifer permeability coefficient and water yield, as well as the source sink term composed of precipitation infiltration recharge and groundwater extraction, on the numerical model of seawater intrusion. The results show that the development of seawater intrusion is the most sensitive to precipitation infiltration recharge and groundwater exploitation, while the influence of permeability coefficient is relatively minor. Increasing precipitation recharge and reducing groundwater mining output can effectively reduce the scope of seawater intrusion in the future. Keywords: seawater intrusion numerical model; coastal aquifer;global sensitivity analysis; SEAWAT; Dagu River Basin