Abstract: In this article we set up a three-dimensional numerical model to simulate mountain-induced mesoscale atmospheric circulation and discuss the role of surface friction in the evolution of this circulation. The results show that under condition of weak baroclinicity, the surface frictional effects promote separation and are favorable of the formation of depole of lee vortices, but under strong baroclinicity condition the surface frictional effect depresses the separation and weakens the strength of lee vortices. However, the extendon of lee vortices and returned flow are enlarged. Though the lee vortices are unique in their method, they are controled by different mechanics. One is caused by surface frictional effect, the other is caused by non-frictional dynamical effect. The role of surface friction is contrary in these two mechanics.