With the Wenchuan earthquake-hit area in the upper reach of Minjiang River as the study area, the characteristics of flash flood disaster distribution and driving factors were analyzed first, and on this basis, the flash flood risk zoning was obtained. Results revealed that the flash flood disaster has the following characteristics: (1) dominated by heavy rainfall, the flash floods mainly distributed in the rainstorm areas of Longmen mountain with banding and group-occurring features; (2) the flash floods concentrated continuously in the scope of main earthquake faults; (3) the flash floods distributed in series or parallel characteristics; (4) the blockage of river channel was serious because of collapses and landslides induced by the earthquake, and the critical precipitation of flash flood disasters decreased, resulting in the increase of scale and frequency of flash flood disasters and the exacerbation of the disaster. According to the rainstorm driving factor (the mean annual maximum precipitation in 1 hour) and earthquake driving factor (distance from the earthquake fault), the areas hit by flash flood disaster in the upper streams of Minjiang River can be divided into three zones: high risk area, moderate risk area and low risk area. The research results provide technical support for the monitoring and early warning of flash flood disasters, proposing targeted flash flood disaster prevention system and reducing the loss of flash flood in mountain areas.