Mirror milling has become an effective way to achieve high quality and green processing of large cylindrical thin-walled parts for aircraft parts like rocket fuel tanks. During processing, the feed rate ratio of milling cutter and support head is changing, which will directly affect the quality of workpiece. Both extending a virtual length of cutter and deducing the parametric equations of speed of the end effectors based on true cutter length could make the feed rates of end effectors keep a ratio to stay mirror symmetrical to workpiece. Then we can get the relationship between feed rate of end effectors and the speed of dual-robot joints based on kinematics analysis, and mirror milling could be realized by controlling the joints parameters of dual-robot directly. At last, the effectiveness of the feed rate planning of mirror milling is verified by simulation and experiment.