Abstract: Aiming to solve the limitation of insufficient spatial characterization of rainfall data for small and medium-sized rivers in mountainous regions, it takes the Hongling River in the mountainous area of southern Anhui as the research object. The PRISM spatial interpolation technique is applied to construct a PRISM-SWAT integrated rainfall model, which is used to simulate key hydrological components including surface runoff, evapotranspiration, and soil moisture content. Results indicate that the PRISM technique enables precise delineation of rainfall heterogeneity in mountainous areas. The PRISM-SWAT model yields simulation results that are most consistent with measured values: the discrepancy rates between simulated and observed surface runoff and soil moisture content are merely 0.6% and 0.73%, respectively, while the mean absolute error (MAE) of the integrated evapotranspiration interpolation data is only 1.55 mm. Furthermore, the model accurately captures the intra-annual unimodal distribution pattern of surface runoff, and its simulations of the spatiotemporal variations in actual evapotranspiration and soil moisture content exhibit a high degree of consistency with the underlying surface characteristics of the watershed.