Abstract: In order to study the influence of fixtures and support forces on the mirror milling chatter of thin-walled parts, a mirror milling chatter prediction model is established. By combining with modal experiments and finite element simulation, the effects of different clamping methods and different support forces on the frequency response are elucidated, and then the effects on the stability of mirror milling are further studied. When the number of fixtures is increased, the amplitude of the higher-order frequency response gradually increases, and the stable region in the stability lobe diagram also gradually increases. When the support force is increased from 0 N to 400 N, the frequency response of the workpiece increases firstly and then turn to stabilizes, and the stable region of the low-speed in the stability lobe diagram increases continuously with the increase of the support force, and the stable region of the high-speed increases more obviously at first, and then its increase decreases gradually. Finally, the mirror milling experiment is used to verify the stability lobe diagram, by comparing the surface morphology, time domain and frequency domain acceleration signals, the chattering situation corresponds to the stability lobe diagram, which verifies the validity of the chattering prediction model of mirror milling processing.