Permanent magnet vernier machines, PMVM, generate a large torque per armature current and have a large torque characteristic at low-speed. Hence, the PMVM is suitable for direct-drive systems. However, the design of the PMVM is difficult because the PMVM is susceptible to the magnet saturation in the iron core. This paper introduces a design method of the PMVM based on the principle of torque generation. First, the theory of the PMVM is described, and then the torque equation is shown. Next, it is considered to increase the torque without changing the machine volume. For that purpose, three methods were investigated: increase of total electric loading (armature mmf), increase of the inner diameter of stator, and optimization of both. As a result, two design methods were obtained: the method to increase torque per current, the method to obtain higher maximum torque by alleviating the magnetic saturation.