Abstract: In order to estimate the impact of population and economy of Sichuan by flash flood,this article based on Digital Elevation Model(DEM) of Sichuan and the judging criteria of flash flood ditch,extracted flash flood ditches of Sichuan Province. And then combined the relationship between slope and precipitation,this article established the Sichuan flash floods risk assessment model. With selected 21 flash floods hazard occurred from January 2011 to December 2013 as a sample data,this article used Sichuan demographic and economic dataes for multiple linear regression calculation of 2013 establish a model that assessment the impacted on the population and economic of flash flood. Get the following conclusion:(1) Extracted 64346 flash flood ditches that affected human life and property safety,which mainly distributed in the mountain around the Chengdu plain,the western plateau of Sichuan and Panxi Region. They affected an area of about 380,000 km²,which accounted for 78% of the area of the province.(2) Established flash floods risk evaluation models,the evaluation results could warn the risk level and region on flash flood.(3) Established forecast models that flash floods' influence,and the evaluations results of influence models on population were more reliable.