Abstract: In order to explore the impact of the monsoon on the pollution in the Liaodong Bay, this paper uses MIKE21 model to carry out numerical research based on unstructured grid. The model uses conservative substances as tracers to calculate the pollutant distribution under the coupling effect of monsoon and tidal current. The wind field is derived from the NCAR assimilation data, and August in summer and December in winter are selected as typical months according to the characteristics of monsoon in the Liaodong Bay. Pollutant diffusion in winter and summer is calculated and discussed under three conditions with no wind, real-time wind, and monthly average wind, respectively. At the same time, in view of the current pollution situation of Liaodong Bay, taking the monitoring data of inorganic nitrogen in the summer of 2022 as the initial condition, the diffusion of inorganic nitrogen under the above three conditions was calculated. The results indicate that the monsoon will accelerate the overall diffusion of pollutants in the bay, but there are differences in the impact of winds of different directions on the pollutant distribution. The research results have reference significance for the pollution assessment and prevention of the bays in the monsoon climate zone.