A heavy rainfall process during 4th-6th July 2003 over the Huaihe River valley was simulated by the Mesoscale Model for Weather Research and Forecasting(MMWRF).The results of diagnostic analysis show that the distribution of the rainfall belt was simulated successfully by the MMWRF model,but there was a deviation in the location of the heavy rain center.The genesis,development,intensification and decay of theme soscale synoptic system during the process were also fairly simulated.