Effects of the mixed layer depth, windspeed and stability on winter surface SO₂ con-centration distribution in the city of Yinchuan, NW China are investigated by use of the solutionof Eulerian advective diffusion equation together with the closed scheme of K-mode l.Resu ltsshow that the surface concentration would be reduced by 40%～75% under the extremely unsta-ble stratification(category A) if the depth increased by 250 m, compared to 20% reduction witha 200 m increase in the case of stable stratification(category F).The strongest diluting effect isrevealed: the SO₂ concentration will be diminished by 90%in the west part of the old city as themixed layer depth grows by 250m and the wind by 3.8m·s^-1, and when atmospheric stratifica-tion changes from category F to A and maxima of the depth and wind are confined to 650m and 4m·s^-1, respectively.