Abstract: Typhoon-induced rainfall is typically intense, short-lived, and highly responsive, often leading to severe flood disasters. Accurate simulation of reservoir inflow during typhoon events is therefore critical for scientific reservoir operation and flood control. In this study, a semi-distributed inflow simulation model was developed based on the General Unit Hydrograph (GUH) theory. Two parameterization strategies were designed and evaluated: sub-basin-specific parameterization, where each sub-basin is assigned its own parameter set, and basin-wide parameterization, where all sub-basins share a common parameter set. The Hedi Reservoir Basin in Guangdong Province was selected as the case study area and divided into eight sub-basins with hourly rainfall data extracted for each. Six representative typhoon events from 2006 to 2013 were used for model calibration and validation. The results showed that the GUH model with sub-basin-specific parameterization consistently outperformed the basin-wide scheme across all validation events, achieving an average Deterministic Coefficient (DC) of 0.71 and demonstrating good generalization capability. Moreover, the GUH model maintained structural simplicity, delivered stable simulation performance, and captured flood peak responses reasonably well. Given its relatively low data requirements and robust simulation ability, the model exhibits strong potential for application in real-time reservoir operation, flood mitigation, and rainwater resource management.