The thin-walled part’s stiffness is very low, so there will be the phenomenon of chatter for various disturbances in the milling process. The accuracy and surface integrity of part become very poor. After the dynamic displacement and dynamic cutting force were analyzed, the dynamic model of process system and the transfer function of regenerative chatter system are built in the side-milling of thin-walled part. Based on above theory, the modal of process system was analyzed by finite element modeling (FEM)，and the stability lobe figure also was plotted, which provided reference for optimization of cutting parameters. Finally the cutting experiment is conducted to verify the built dynamic model and method are correct and feasible to prevent chatter during cutting.