Due to magnetic gearing effects, spoke-type permanent magnet vernier machines (ST-PMVMs) have the merit of high torque density, where an extra torque amplification coefficient, i.e., pole ratio (the pole-pair ratio of PMs to armature windings) is introduced. However, different from surface-mounted PMVM, the variation of torque against pole ratio in ST-PMVMs is non-linear, which is increased at first and then decreased. This article is devoted to identify the optimal pole ratio of ST-PMVMs by equivalent magnetic circuit model. It is found that except the P r