Abstract: In order to reduce the weight of parts, aeronautical parts are often designed as thin-walled parts. During the machining process of thin-walled parts, machining chatter vibration is prone to occur, which affects the machining quality and efficiency. This paper proposes a method to suppress the machining vibration of thin-walled parts by increasing the system damping ratio through the use of liquid damping medium. A frequency response function model considering the equivalent damping of the liquid medium was established, and modal tests of thin-walled parts with the application of liquid medium were conducted to obtain the modal parameters of the system. Based on the acquired modal parameters, a predictive model for machining system stability was established to predict and analyze the stability of the machining system. The results show that the equivalent damping of the liquid medium can reduce the acceleration response of the system, improve the stability of the machining system, and effectively suppress chatter vibration in milling operations.