To better understand and improve the forecast performance of the rainstorm in Guang''an city, the authors explored the weather circumstance of 34 precipitation processes (including 14 rainstorm cases) with moderate precipitation and beyond occurred in Guang''an city during period 2015-2017 by employing the precipitation data from the ECMWF high-resolution numerical forecasting model (hereinafter referred to as ECMWF), 4 national observation stations in Guang''an, and 160 regional auto stations. The result shows that a direct forecasting of rainstorm based on the ECMWF rainstorm forecast output would result in a missed report and a low score. However, when the ECMWF forecast satisfies one of the following four correction conditions: medium and short-range forecast R ≥ 50mm, medium-range forecast R ≥ 25mm and short-range forecast R ≥ 50mm, medium-range forecast R ≥ 50mm and short-range forecast torrential rain R ≥ 25mm, and both the medium and short-range forecast R ≥ 35mm, the forecasting of torrential rains will be carried out with a high score, and a low rate of missing reports, and a high hit rate, which can effectively improve the forecast quality. And it is also suggested that the ECMWF shows a good forecasting skill in the forecasting of rainstorm duration, strong precipitation period, falling area of rainstorm, and area rainfall amount.