Abstract: The construction of "three lines of defense" provides a solid data foundation for flood forecasting and brings new opportunities to improve the level of flood forecasting in the basin. This paper compares the performance of weather radar in Fujian Province, X-band rain radar and hydrological monitoring station in Quanzhou city in capturing the magnitude and spatio-temporal distribution of heavy rain. The multi-source rainfall data fusion method based on neural network is used to generate the fusion rainfall data, which improves the detection ability of precipitation events and is coupled with hydrological and hydrodynamic models to realize the rapid simulation of flash flood process. It can provide support for flood control and disaster reduction in small and medium-sized watersheds.