Abstract: The difficulty of prevention and control of flash flood disasters is that the relationship of rainfall, dis-charge and water level is complicated and inter-changing, and the early warning model based on rainfall condi-tions derived from disastrous water level is unable to reflect the intrinsic rainfall and runoff process. Based on the investigation of flash flood disasters in the small watersheds of Fuxing River in Chongqing, this paper adopts the rainfall driving index method, fully considering the influence of rainfall intensity and early rainfall, establishes an early warning model based on the relationship between rainfall intensity and effective cumulative rainfal, and pro-poses the rainfall driving indicator 2 000 as an immediate transfer indicator, 1 800 as an early warning indicator, which provides a scientific basis for flash flood disaster prevention and control in small watersheds.