Abstract: Non-point source (NPS) pollution is characterized by hidden occurrence, hysteresis effects, and spatial heterogeneity, and quantifying its load and identifying key source areas remains a challenge for watershed water environment management. This study established a hydrological and water quality model of the Xuebu River Basin based on the SWMM model, quantitatively simulating water levels and water quality at the Sanxingqiao section from 2022 to 2023, as well as pollution loads from 25 sub-watersheds. By designing rainfall scenarios with return periods of 1 year, 5 years, 10 years, as well as land use change scenarios (increasing or decreasing farmland, forest land, and village areas by 5% and 10%, respectively), the study identified the response of NPS pollution to changes in land use and rainfall in the Xuebu River basin. The results indicated that watershed NPS pollution exhibited significant spatial heterogeneity, with the midstream region being the most severely polluted due to dense towns and farmlands. Farmlands were the primary sources of pollution, producing total nitrogen (TN) of 455.47 t/a and total phosphorus (TP) of 53.17 t/a. The per unit area TN and TP loads of farmlands reached 99.55 kg/(hm²·a) and 11.62 kg/(hm²·a), respectively, which were significantly higher than those of forest lands (50.20 kg/(hm²·a) for TN and 7.02 kg/(hm²·a) for TP) and villages (30.87 kg/(hm²·a) for TN and 7.34 kg/(hm²·a) for TP). With increasing rainfall intensity, under the 10-year return period scenario, the TN and TP pollution loads produced in 1 hour are 54 t and 22 t, respectively, representing an increase of 39% and 46% compared with the 1-year return period scenario; peak concentrations at the Sanxingqiao section did not rise synchronously due to runoff dilution, while the peak arrival time was advanced by 11 to 30 minutes. Land use change scenarios showed that farmland changes dominated TN load fluctuations, while forest land changes dominated TP load fluctuations. Increasing forest area effectively reduced pollution loads in most sub-watersheds. Finally, it was recommended to implement the source-process-end integrated control strategy in the midstream region of the Xuebu River Basin and optimize the conversion ratio of farmland to forest land to achieve effective reduction of watershed NPS pollution.