Abstract:The effect of terrain level on the precipitation in the Yangtze-Huaihe area is investigated by use of MM5v3 model, the change of precipitation is studied from raising and decreasing the terrain level in the model.The cases are the heavy rains on June 28,1998 and June 12, 1991, 24 hours simulations are performed, and the variations of vertical velocity, vorticity, divergence, moist potential vorticity and moist flux etc are also analyzed.The results show that all these factors are changed when the terrain level is changed, and then the variation of the precipitation can be influenced.Since all the factors can influence the precipitation,in order to predict the effect of the terrain on precipitation, all the factors must be considered.On the whole, the change of precipitation caused by terrain only occurs near the area of terrain change, the precipitation increases obviously in the upwind direction of the mountain.The main factor controlling the place and strength of the precipitation is the macro- and meso-scale circulation, the terrain can change the place and strength of precipitation.