The theory of watershed runoff generation and concentration is an important basis for hydrological forecasting. Generalized unit hydrograph proposed in 2021. The generalization of the watershed's contribution to net rainfall storage as M equivalent linear reservoirs in parallel provided a new method for catchment calculation and had been applied in countries such as Europe and the United States. To test its applicability in flash flood simulation, four small tributaries of Huaihe and Yangtze rivers were selected as the study objects and the rainstorm flood process was compared with Nash unit hydrograph method. The results had shown that the simulation reached the standard of Class B accuracy requirement, but from the evaluation indexes, the average Nash efficiency coefficient, peak present time and its passing rate of the generalized unit hydrograph (0.79, 0.90 h, 98.30%) were better than the Nash unit hydrograph (0.75, 1.09 h, 94.34%). Moreover, it integrated the topographic and geomorphological features of the watershed, which can better characterize the watershed catchment characteristics and has strong applicability, providing a new idea for domestic flash flood hazard warning and forecasting.