Magnetic gears, which can transmit torque without mechanical contact, have low vibration and acoustic noise, and are low maintenance in comparison with conventional mechanical gears. Various types of the magnetic gears have been introduced. Among them, a planetary type magnetic gear has attracted interest recently because its transmission torque is higher than the other types. This paper presents a high-speed and accurate optimal design method of the planetary type magnetic gear based on reluctance network analysis (RNA). The RNA has several features including a simple analytical model, high calculation accuracy with high speed, and ease of coupled analysis with rotational motion of rotors. The validity of the proposed method is proved by comparing with a finite element analysis (FEA) and experiment.