Abstract: A numerical modeling of precipitation in the south area is conducted just by changing the terrain data of underlying surface.The simulation results are as follows: 1) The difference is the most significant in a sudden change of terrain.2) The location and secondly intensity of precipitation are effected directly by the tiny change of terrain.3) The shortwave radiation is influenced directly when the terrain is changed,and sensible /latent heat fluxes eliminate and replace each other.4) When there is precipitation in Sichuan Basin,a southeast wind prevails in the lower layer and can result in cyclonic curvature in the basin.Convergence will remarkably occur in the windward slope and divergence in the leeward slope.5) Terrain gradient also influence the development of convection.The ascending motion occurs much easier in the steep terrain and the milder the slope,the more powerfully the current climbs.In a word,a tiny change of terrain can already influence the location and the intensity of precipitation obviously.