Aiming at the problem of low machining quality caused by unreasonable selection of robot milling station for large composite components, a single robot multi-station milling station optimization method based on optimal stiffness is proposed. The stiffness of the robot is obtained by the forward and inverse kinematics of the robot, and the stiffness function model related to the robot position is established. The robot milling tasks at different stations are allocated, and the robot milling station optimization research is carried out through the stiffness-based station optimization algorithm to obtain a set of stations with the best robot stiffness. The optimization effect of robot milling position is verified by robot milling experiment. The results show that the station optimization based on the optimal stiffness can significantly improve the stability of the robot milling edge, and reduces the surface roughness of the milling edge by more than 33% compared with before optimization.