In the medium range forecasting system for heavy rain,the ECMWF 500hPa height predictions are corrected with Kalman filter method. The approach was put into the operational application in the summers of 1996 and 1997. The results show that the approach is effective and the forecast accuracy is improved. In this papper,the correction method is introduced,and experiments of correcting ECMWF 500hPa height predictions are made,the root mean square errors of uncorected and corrected 500hPa height predictions are analyzed and compared.