Abstract: In this paper, a 3-dimensional numerical model was set up and used to compute the surface concentrations of SO2 in the coastal region of Qinhuangdao city as the land-sea breeze prevailing. The atmospheric diffusion equation was solved by using the method of fractional steps, the techniques used to represent terms involving the derivatives in the spatial coordinates of these differential equation including; pseudospectral method in horizontal, upstream and Crank-Nicolson method in vertical. The computed 24-hour averaged surface concentrations of SOZ over this region showed a good agreement with the observed values. The computed tendency of diurnal variation of SO2 concentrations at port station coincides fairly well with observational ones. The analysis showed that the performance of the model in this paper is good and numerical calculation is stable.