In order to solve the problem of low power factor of vernier motor, a motor design optimization concept to improve the power factor is proposed. Firstly, the winding function approach is used to calculate the inductance of fractional slot centralized double-layer windings, to derive the expression for the power factor of the vernier motor, and to analyze the main design parameters affecting the power factor. Secondly, combined with the finite element method to study the change rule of motor performance when each design parameter is changed, and then summarize the design concept. Then, a cleft tooth vernier motor is taken as the benchmark prototype, a motor with high power factor is redesigned according to the proposed concept, and a genetic algorithm is used for multi-objective optimization of the main design parameters of the motor. Finally, the performance comparison with the benchmark prototype motor shows that the power factor of the designed motor is higher, which verifies the validity of the theoretical analysis and the proposed design concept.