Facing the severe challenges of synergistic resource optimization and regional high-quality development, a multi-objective optimization model for the water-energy-food nexus system at the county scale was developed for the Hengyang-Shaoyang Arid Corridor. The model was constructed based on the NSGA-Ⅲ algorithm by considering social, economic, and ecological benefits under current and future scenarios. The optimal allocation schemes under different hydrological years were identified using the entropy weight-TOPSIS method, and key drivers affecting regional benefits were explored using the Geodetector. The results showed that a 1% increase in water supply could increase the comprehensive benefits by 3.875% to 7.650% in the current scenario. By optimizing crop structures and reallocating water resources, competition among sectors was alleviated, achieving synergistic improvements in social, economic, and ecological benefits. Under the future normal-flow scenario, crop structure optimization and water redistribution increased annual grain production to 9.2885 million tons, exceeding the per capita standard by 24%, while reducing COD emissions by 9.8%. Under the dry-year scenario, the food security threshold can be maintained by reducing the planting area of high-water-consumption crops, with annual grain production exceeding the standard by 12.9%. Regarding driving effects, influencing factors were more dispersed in normal-flow years but became significantly concentrated in dry years. The explanatory power of multi-factor synergistic effects on social, economic,and ecological benefit variations was substantially enhanced, indicating that the synergistic effect between water supply security and resource allocation equity was the key mechanism driving the evolution of target benefits in the Hengyang-Shaoyang Arid Corridor.