In the manufacturing process of complex thin-walled parts, the removal of thin-walled materials will change the structural modal parameters. The conventional dynamic response analysis often ignores the modal changes, which leads to the deviation of the predicted vibration deformation under the action of periodic milling force. Therefore, based on the matrix perturbation theory, this paper analyzes the influence of material removal on the modal parameters of thin-walled parts, obtains the modal parameters of thin-walled parts processing, and compares with the simulation results of commercial finite element software, realizes the accurate calculation of modal parameters of thin-walled parts in the process of material removal, and provides a theoretical basis for analyzing the vibration deformation of thin-walled parts processing.