A double-layer permanent magnet spherical motor (PMSM) with same spatial distribution of stator poles and rotor poles is designed based on spherical harmonic theory in this paper. The stator coils are equivalent to permanent magnets to simplify the calculation, and the torque model based on virtual work method is derived. Firstly, the torque model of single pair of poles is derived on the premise of considering the fundamental component of the magnetic field. Then, the relative positions of stator poles and rotor poles, the direction angles of torque components are discussed. Finally, the torque model is obtained by space vector theory and superposition theorem. Moreover, the simulation and experiment are implemented to verify the feasibility and correctness of the proposed torque model. The obtained torque model in this paper has similar expression with that of traditional motor, which lays a theoretical foundation for the structure optimization and control strategy of PMSM.