Abstract: In the rainstorm disaster pre-assessment service, a model precipitation accuracy that accurately describes the catastrophic rainstorm is needed. In the paper, a new method was designed for calculating the accuracy of precipitation based on the pre-assessment of rainstorm disasters. The main features of the method include:to increase the weight of the large precipitation that hits the severe rainstorm, and reduce the weight of the small precipitation; and punish the accuracy of precipitation when the model forecast precipitation and observed precipitation are respectively located on both sides of the rainstorm threshold in the formula. First, through a ideal test, the rationality of the formula and the sensitivity of the parameters are analyzed. Then the method is used to test and analyze one rainstorm. The relationship between the model precipitation and the observed precipitation is verified, and the rationality of the method and the characteristics of the large precipitation right in the formula are proved. Finally, the method was used to statistically analyze and test the precipitation accuracy of ECMWF model and NCEP model, and compare with TS score to verify the rationality of precipitation accuracy. The precipitation accuracy in batch test shows that the ECMWF model has a better guiding significance for the pre-evaluation service of rainstorm disasters.