In the field of orbital belt sanding technology, in order to solve the problem of belt deflection research has mainly focused on on-site treatment measures, often ignoring the mechanical nature and dynamics of the movement, as well as other influencing factors. The nature of the belt deflection phenomenon was analyzed from a mechanical properties. The deflection mechanism, attributed to the uneven distribution of tension within the belt, was revealed. It was determined that belt speed, tension, and width are the key factors affecting the deflection of abrasive belts. A rigid-flexible coupled nonlinear virtual prototype model of the rail belt sanding system was constructed in order to investigate the effects of rail belt sanding rotational speed and sanding position on the belt's lateral displacement, speed, and acceleration through simulation experiments. The outcomes of the rail belt sanding experiment aligned with the findings of the simulation analysis, thereby substantiating the precision of the simulation results. The findings indicate that the grinding position of the rail belt represents the most significant factor influencing the occurrence of belt deflection, followed by grinding speed as the next most influential parameter. Based on the study results, optimised process parameters were proposed, and it was recommended to limit the belt sanding speed to less than 3 000 r/min and to adopt the method of sanding at the centre of the belt in order to effectively prevent and mitigate the phenomenon of belt deflection.