The RFPM(Radial Flux Permanent Magnet) generator has numerous advantages such as high output voltage and output power, high efficiency, manufacture easy but the slotted RFPM generator configuration produces the cogging torque. The cogging torque would be the source of acoustic noise and vibration. This paper presents the electromagnetic structure design analysis and the cogging torque reduction design of RFPM generator. It is composed of the inner stator and the outer stator and internal rotor. We called it as DG-RFPMG(Dual Generator-Radial Flux Permanent Magnet Generator). Firstly, the design of the pole-arc ratio of rotor magnets to reduce cogging torque is studied. Secondly, the design of the stator displacement of the outer stator and the inner stator to reduce the cogging torque is studied. Finally, the combined design optimization considering both the pole- arc ratio and the stator displacement to reduce the cogging torque is studied. The design of DG-RFPMG was calculated by 2D FEM(Finite Element Method).