A two-dimensional stationary model is used to examine the dynamical effects produced by the flow over mountainous areas of three horizontal scales. Results from numerical simulation show:(1)large-scale orograph may produce subsidence of air flow upstream of the mountain ridge, thus resulting in dry climate;(2)meso-scale mountain ranges may cause wave motion downstream which may influence aircraft in flight;and(3)small-scale hilly areas(or architectural complexes)may have some influence on the aerosol diffusion in the flow. A better knowledge of the characteristic features of the small-scale orographic flow would help to plan the rational distribution of factories in the mountainous areas and the proper sitting of the rice seedling beds during the seedling stage.