Since flood is formed by storm, flood forecasting is the continuity of precipitation prediction. In recent 30 years, numerical weather prediction has made great advance, but the attempt to apply watershed hydrological model in flood forecasting is slow. The reasons for the different accuracies between numerical weather prediction and flood forecasting are investigated. Successful experience of numerical weather prediction and the problems of watershed hydrological model in the application of flood forecasting are discussed by means of comparison of the weather model and the watershed hydrological model. Problems discussed are the prediction methods and the forecasting time, the initial fields and the boundary value fields, data assimilation and data fusion. It is expected that great inspirations to flood forecasting can be obtained from the successful experience of numerical weather prediction. In the near future, seamless connection can be realized between weather prediction and flood forecasting, and as a result, the accuracy of flood forecasting can thus be improved and the forecasting time can be extended.