To improve the machining quality of mirror milling of thin-walled parts, this paper proposes a collaborative motion control strategy for mirror milling of dual hybrid robots. Firstly, based on the characteristics of robot motion control, an open CNC system with a dual CPU master-slave control architecture is developed to achieve human–computer interaction and motion control. Then, in order to achieve dual robots collaborative motion and improve the machining quality of thin-walled parts, four key technologies are integrated into the CNC system, namely mirror path generation of dual robots, synchronous speed planning, collaborative kinematics, and real-time compensation of motion errors. Finally, based on the independently developed integrated mirror milling CNC system, flat thin-walled part slot milling experiments with single and multi-point support, dual robots collaborative and non collaborative machining, multipoint support surface milling experiments, high curvature path high-speed collaborative motion experiments, and curved thin-walled part slot milling experiments are carried out. The experimental results show that the proposed collaborative motion control strategy can ensure high synchronization position accuracy of the dual robots. In addition, the multi-point support method can improve the vibration stability of workpiece milling while ensuring the wall thickness of thin-walled parts.