Abstract: Flash flood disasters have the characteristics of wide impact and serious harm, and have become a prominent problem in disaster prevention and mitigation. Taking Longquan Gully in Huairou District, Beijing as an example, based on field investigation and topographic mapping, the control section and critical water level were determined. By constructing the MIKE11-NAM coupled model to obtain the water level-flow relationship and rainfall-flow relationship, the rainfall warning indicators for 1 h, 3 h, 6 h, 12 h and 24 h under different soil water content conditions were proposed as immediate transfer indicators.MIKE FLOOD was used to realize the MIKE11-21 coupling model to simulate and analyze the inundation risk of the ditch under different soil water content conditions, rainfall calendar times, and rainfall levels, and the results showed that the flood control capacity of Longquan Gully was insufficient. It provides a reference for determining the early warning indicators of other flash flood basins in the city, as well as the compiling of flash flood disaster plans, forecasts and early warnings and risk avoidance transfer.