Composite insulators operating in sandy desert areas are susceptible to erosion from high-speed wind and sand flow, leading to increased surface roughness of the shed skirt and edge wear, which results in reduced insulation performance and significantly shortened operational life. To address the wear issue of composite insulators in severe wind and sand environments, a numerical simulation method was employed to establish a sand erosion simulation model based on Finnie theory. This study examined the erosion-wear characteristics of the shed skirt surface under different wind speeds, sand particle sizes, and suspension methods. The results indicate that the erosion wear rate of the composite insulator surface increases with rising wind speed, exhibiting a nonlinear growth pattern. When the wind speed reaches 25 m/s, the wear rate suddenly increases. As the sand particle size increases, the wear rate of the shed surface also rises, and the maximum erosion wear rate tends to stabilize when the particle size reaches about 300 μm. Under the V-type string suspension method, the maximum wear rate of the shed skirt surface is similar to that of the I-type string; however, the insulator’s suspension method primarily affects the area subjected to wear. Due to the unique flow field characteristics of inclined suspension, both the average wear rate and wear area of the V-type string’s shed skirt are greater than those of the I-type string. The research findings provide a reference for the optimization design of composite insulator structures in wind-sand environments.