Abstract: In order to construct a reasonable assessment index for Sichuan rainstorm-disasters (referred to as:an assessment index).In this paper,eight precipitation factors are selected to characterize the characteristics of 126 rainstorm-cases of Sichuan region from 2008 to 2018,we used the overall principal component and threshold method to establish the weight and threshold of the factor,then an assessment index was established.Through the inversion of historical cases and application of forecasting examples.The results showed that:(1) the average rainfall value in the rainstorm area,the area of ≥25 mm/h and the area of heavy rainstorm are the key factors,which affect the ability of Sichuan heavy rain disaster.The evaluation index constructed by using principal component analysis better reflects the disaster-causing ability of previous rainstorms,when the index reached 0.8 or above,it generally corresponded to Severe rainstorm disasters.(2) Combining economic loss and a standard of meteorological disaster assessment and classification,the evaluation index is classified into 4 levels.Based on this,the forecast precipitation data of 5 km×5 km corrected by the Sichuan Meteorological Observatory at 08:00 and 20:00 daily was input the assessment index model,then calculated the future index values and the spatial distribution of the corresponding disaster-prone area.The practical application showed that the evaluation index model has a significant practicability for assessing the overall disaster mitigation capacity of the rainstorm process and the spatial distribution of the specific stormwater disaster mitigation capacity.