Abstract: With the rapid development of the aerospace field, large parts are applied more and more widely. In view of the difficulties in real-time monitoring and insufficient intelligent detection of large thin-walled free-form surface insulation layer machining, a framework of free-form surface machining system based on digital twin technology was proposed. Combining the key technologies of high-fidelity twin model construction, multi-source dynamic data acquisition, virtual-real mapping, equipment debugging, and feedback control, a digital twin system for large-scale complex surface processing was developed to realize the monitoring and debugging feedback of free-form surface processing. Finally, the feasibility and effectiveness of the proposed method were verified by an engineering example.