Abstract: The traditional early warning of rainstorm flash flood mainly relies on the rainfall data of the ground rain gauges, which is prone to false and missing alarms or difficult to meet the warning timeliness.Therefore, moving forward the flash flood warning response time and monitoring the area rainfall of the watershed are important technical means to meet the goal of flash flood defense, and the application of rainfall radar technology provides a new early warning idea for flash flood defense.In this paper, a rainstorm flash flood disaster in Liulin Town of Suizhou City of Hubei Province on August 12 of 2021 is taken as an example.The modular distributed hydrological model (MDHM)is used to simulate the flash flood process and carry out early warning analysis.The effectiveness and reliability of the flash flood early warning under the two rainfall data sources are evaluated by comparing the disaster warning timeliness under the rainfall input conditions based on the rainfall radar and the ground rain gauges.It is found that the rainfall forecast by the rainfall radar combined with the early warning of steep rise rate of water level can significantly improve the early warning effect and provide technical reference for flash flood management.