With the development of electric vehicle, there were more and more old motor which would be replaced and obsoleted, it was also necessary to study the remanufacturing of the old motor. In order to improve the performance of the motor, the optimization of the outer circle of the rotor was used to reduce the saturation magnetic density area and optimize the air gap structure. How different eccentric circle effect on cogging torque was analyzed, the changes of performance of the old motor and the remanufacturing motor were compared. The magnetic flux density of motor harmonic and cogging torque trend with the different of chamfering circle was researched. The result showed that the cogging torque increased first and then decreased with eccentric circle increasing, chamfering circle had little influence on harmonic. Under the rated conditions, when the eccentric circle of remanufacturing motor was 36 mm and the chamfering circle was 4 mm, core loss of remanufacturing motor decreased by 6.55 W/kg, efficiency increased by 0.05% and output torque was reduced by 4%. The remanufacturing motor was made to reduce the loss and increase the efficiency, the output torque was reduced.