Abstract: Hydrological models for simulating watershed water cycle processes are critical tools for clarifying water resource evolution characteristics and optimizing watershed water resource allocation. The SWAT model has demonstrated excellent performance in arid and semi-arid regions; however, its application in tropical island basins—where excess infiltration runoff dominates and local saturated runoff occurs—remains limited. To address this gap, it improved the SWAT model by optimizing modules for river network extraction, sub-basin division, and meteorological data processing, accounting for tropical islands' complex climatic conditions and basin-specific features(e.g., short, rapid river channels, concentrated rainfall, and unique vegetation cover). A SWAT model was developed for the Wanquan River Basin in Hainan Province, with parameter calibration and validation conducted using data from the Jiaji(2)Station(the basin outlet). Results indicate that during the calibration period(2000-2015), the model achieved a coefficient of determination(R²)of 0.95 and a Nash-Sutcliffe efficiency(NSE)of 0.95;during the validation period(2016–2022), R² and NSE were 0.86 and 0.84, respectively. The simulation error of flood peak discharge during the flood season was within 15%. These findings confirm the good applicability of the improved SWAT model for hydrological process simulation in the Wanquan River Basin.