Abstract: Identification of Priority Management Areas (PMAs) and evaluation of the effectiveness of Best Management Practices (BMPs) provide an important basis for precise control of agricultural nonpoint source pollution and scientific decision-making. Taking the Zheshui River Basin of Dongjiang Lake as the study area, this study applied the SWAT model combined with scenario simulations. PMAs were identified by comprehensively considering nitrogen and phosphorus flux, population density, and water quality requirement factors, and the pollution reduction efficiency and cost-effectiveness of BMPs were evaluated. The results show that the nitrogen and phosphorus loss loads ranged from 8~15 kg/hm² and 0.15~0.70 kg/hm². PMAs accounted for only 9% of the total basin area but contributed approximately 30.7% of the nitrogen flux and 43.7% of the phosphorus flux. Among the PMAs, 94% were cropland, indicating that agricultural activities coupled with high hydrological connectivity constitute the key driving mechanism of nonpoint source pollution in the basin. Simulation results of BMPs indicate that among single measures, a 20% fertilizer reduction achieved the best performance, with nitrogen and phosphorus reduction rates of 10.1% and 26.5%, respectively, followed by grassed waterways, vegetative filter strips, and zonal tillage management. Combined measures further improved reduction effects, and the four-measure combination achieved the highest reduction rates of 16.8% for nitrogen and 41.6% for phosphorus, although it also incurred the highest cost. Cost-effectiveness analysis shows that cost-effectiveness declines as the number of combined measures increases. Vegetative filter strips exhibit the best economic performance among single measures, while the combination of 20% fertilizer reduction and vegetative filter strips achieves the optimal balance between reduction efficiency and cost-effectiveness. The results provide scientific support for regional agricultural nonpoint source pollution control and refined watershed management.