The transregional flow of ecosystem services (ESs) results in the diffusion of ES benefits. Many National Key Ecological Function Areas (NKEFAs) are located in northwestern China, which faces a high risk of wind erosion. Therefore, the windbreak and sand fixation service (WSFS) is important not only for the local NKEFAs but also for the downwind areas. This study assessed the benefit diffusion process of the WSFS in NKEFAs by combining the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) and the Revised Wind Erosion Equation (RWEQ) models. In 2010, 1689 WSFS diffusion paths were simulated first by using HYSPLIT, with the path directions varying from northeast to east and southeast and passing through most areas of northern China. By interpolating the diffusion paths, the beneficiary areas of the WSFS amounted to 617.81 × 10⁴–1570.99 × 10⁴ km² in 2010 and spread beyond China, mainly extending to the East Asian region. Incorporation of the RWEQ model showed that the amount of WSFS benefit diffusion from each NKEFA varied greatly and was mainly concentrated in northeastern, central or northwestern China. In addition, the distribution frequency of the diffusion paths and the benefit diffusion effects exhibit obvious distance attenuation characteristics. Based on this study, we can establish a direct connection between the WSFS in the NKEFAs and the downwind beneficiary areas and provide a reference for the interregional ecological compensation policy, thereby guaranteeing the sustainable development of both wind erosion areas and the downwind affected areas.