In this paper, a pole-piece shape is proposed. We want to improve the low torque characteristics of the magnet gear and the large torque ripple problem. For the pole-piece design, the results were analyzed through the field finite element analysis. The relationship between the design variables and the objective function was analyzed using the Box-behnken method. Therefore the proposed pole-piece design increases the output density of the magnet gear and reduces the torque ripple which affects noise and vibration during gear operation. We also compared the transmission torque characteristics of general pole-piece, conventional magnetic flux concentrating type pole -piece, pole-piece of optimal design. It is confirmed that the pole-piece structure proposed in this paper has superior transmission torque characteristics.