A method of forecasting the heavy rainfall in the Miyun Reservoir Basin is developed,according to the synoptic situation during the heavy rainfall,by means of the interpretation and application of NWF outputs,and the local observations.By analyzing the rainfall data of 20 hydrological stations in the Miyun Reservoir Basin from 1970 to 1993,the relationship between 45 heavy rainfall events and synoptic situations,NWF outputs,the forecast indexes and synoptic patterns are put forward,and 24-hour heavy rain forecast equations of June,July,August in the Miyun Reservoir Basin are developed.The operational forecasts show that the forecast method is feasible and successful.