Abstract: To safeguard the ecological environment and effectively combat seawater intrusion (SI), a variable-density SI numerical model was developed in Longkou City. This model, based on SEAWAT, enables a scientific approach to prevention and control. By conducting scenario analyses, the quantitative assessment of SI's influencing factors was accomplished. Furthermore, measures for groundwater utilization to counter SI were proposed. The study also presents a projection of SI trends from 2018 to 2050. The findings demonstrate that the numerical model accurately simulates the spatiotemporal variations in groundwater levels and effectively captures SI's progression. Evaluation during the testing phase yielded root mean square error (RMSE), mean absolute error (MAE), and mean relative error (MRE) values of 0.903 m, 0.811 m, and 8.78%, respectively, for groundwater levels. Correspondingly, RMSE, MAE, and MRE values for chloride concentration in the monitoring well were 51.61 mg/L, 42.52 mg/L, and 9.61%, respectively. Moreover, the quantitative assessment revealed that groundwater pumping and precipitation exerted significant influences on SI dynamics, with the northern coastal regions, such as Beima Town, being crucial areas for groundwater management. The predictive analysis indicates a declining trend in SI, with an estimated SI area of approximately 128.67 km² by the end of 2050. Consequently, future management strategies should account for the impact of wet and dry years on exploitable groundwater reserves. Additionally, implementing partitioned groundwater management measures can effectively mitigate SI risks. This study holds substantial significance for understanding the evolution of SI, identifying its influencing factors, and ensuring sustainable groundwater development and utilization in coastal regions.