Wind erosion is a key factor contributing to desertification and soil degradation in arid and semiarid regions. After detached from the soil surface, the transportation of wind-blown particles and its impact area are determined not only by meteorological conditions but also by the size of particles. However, models commonly used for assessing the regional impact of wind erosion rarely consider particle size differences, resulting in reduced assessment accuracy. This study adopted a sand dust event of the Mu Us Sandy Land in the southern part of the Inner Mongolian Plateau of China as an example. Based on previous studies involving the simulation of dust transport masses and trajectories, this research integrated the transport characteristics of particles with different sizes and proposed a new method for assessing the impact of wind erosion. The results showed that the wind erosion-induced regional impact integrating the particle size accounts for 7.5% of the total wind erosion impact. Compared to the method without integrating the particle size, the application of the method integrating the particle size reduced the error in modelling particle masses far from the dust source and increased the simulation accuracy for the spatial distribution of dust by 14.29%. The study emphasizes the critical role of the particle size in wind-blown particle transport and provides a new approach for accurately evaluating the regional impact of wind erosion.