Compared with the conventional coaxial magnetic gear, magnetic harmonic gear (MHG) is a device with large transmission ratio. In order to improve the transmission torque, an MHG with double fan-shaped Halbach arrays is proposed in this paper. According to the theory of magnetic field modulation and the unique unilateral effect of Halbach array, both inner and outer permanent magnets (PMs) are arranged in a Halbach array. In addition, all PMs are fan-shaped. The air gap magnetic field and torque of MHG are analyzed by two-dimensional finite element method. Compared with the conventional MHG, the proposed MHG enhances the air-gap magnetic flux density, reduces the air-gap harmonic content, and increases the torque density.