In this paper, by incorporating the new concept of the noncontact magnetic planetary gear into a permanent magnet brushless machine, a new multiport magnetic-planetary-gear permanent magnet machine is proposed. To achieve flexible combination and split of the power and torque among different electrical or mechanical ports in the machine, a multiobjective optimization design method considering multioperational modes is proposed and investigated. To obtain high optimization design efficiency, the whole optimization is divided into three steps based on various driving modes. In each step, the multobjective genetic algorithm, response surface method, and direct screening method are utilized, respectively. Moreover, the basic no-load characteristics and torque performances of the proposed machine are also studied. Finally, a prototype machine based on the optimized structure dimensions is manufactured and tested. Both the theoretical and experimental analysis verifies the effectiveness of the investigated machine and the proposed method.