The work aims to study the clamping deformation of thin-walled annular mechanical packaging parts, in order to optimize the clamping scheme of annular packaging parts to avoid elastic-plastic deformation of the parts during the machining process of such thin-walled annular packaging parts, thus avoiding the scrapping of the assembled parts. The finite element analysis method was used to investigate the behavior of thin-walled annular packaging parts based on ANSYS. Additionally, combined with the "load increment method", a milling preload application scheme was designed to examine the impact of preload on the milling deformation of the parts during the packaging process. The simulation results demonstrated that applying preload force to the roughing bar wall position, employing compression force in the finishing groove, and combining preload force with a torque-limiting wrench effectively minimized the deformation of the thin-walled support ring. The experimental study suggests that employing a torque-limiting wrench to regulate the preload force within the appropriate range, with the action point positioned at the bar wall, can effectively prevent deformation of the thin-walled support ring. In turn, this enhances the product quality of the annular packaging parts.