[Objective] To simulate and verify a flash flood process on June 17, 2016 in Nileke County of Xinjiang Uygur Autonomous Region by a FloodArea model, in order to determine the critical rainfall for flash flood.[Methods] A typical flash flood ditch was taken as the research object. Based on FloodArea model and using meteorological data, digital elevation model data and basic geographic information data in the flash flood ditch of Kemeng Township Nileke County, the correlations between the area rainfall with different cumulative aging and the simulated flood process line was analyzed, and the best set of correlations was used to construct the formula.[Results] It was found that the highest correlation occurred between the submerged depth of the basin and the corresponding 9 hour surface rainfall. The critical rainfall threshold at 4 levels of the 9 h cumulative rainfall was 12.80(forth level), 25.78(third level), 45.24(second level) and 64.71(first level) mm, respectively.[Conclusion] The floodArea model can well simulate the flood process in the study region, and the rainfall at different risk levels of the flash flood can be reflected.