Comparing with the mechanical gear contact transmission,magnetic gear is a new transmission device with a novel structure and a broad development prospect. The large torque transmission is achieved by using the magnetic field modulation principle. On the basis of the traditional magnetic gear structure,the inner and outer rotor permanent magnets are improved,which the inner permanent magnets are triangular-fan-shaped phase and the inner and outer permanent magnets are Halbach arrays. The two dimensional（ 2 D） finite element（ FE） method is used to simulate the modified magnetic gear model,and the electromagnetic field and electromagnetic torque of the magnetic gear are calculated. At the same time,the magnetic field and torque are compared with the conventional magnetic gear. The simulation results show that the output torque of the improved magnetic gear is greatly than the traditional magnetic gear,which can effectively enhance the air gap magnetic density and reduce the air gap harmonic content. It is a great significance to study and apply the torque density of concentric magnetic gear.