Since Numerical Weather Prediction has been operated,the forecast accuracy of upper synoptic situations and weather elements have been improved. Recently,it is a common concerned question to explain and to apply NWP production for forecaster. Based on cluster analysis,the forecast of heavy rain area and it's character of circulation pattern have been studied by the use of NWP production 500hPa height fields and precipitation data. Results show that the method has reference value in the operational forecast. Simultaneously the features of circulation field corresponding to precipitation patterns in China are given.