In order to improve the intelligent operation level of the motor operation mechanism of 40.5kV vacuum circuit breaker, and finish the opening operation of the circuit breaker under the preset stroke curve, the relationship between winding voltage and speed of motor is studied in the running process. The speed control method of motor by controlling the voltage at the specified point is proposed. Aiming at the opening process of circuit breaker, combined with the armature equation and torque equation of motor, motor model is established. The motion characteristic equation about winding voltage of motor, motor speed, stroke of the motor is established. The experiment on the speed control of the motor is carried out. According to the speed requirement of the preset curve at the multiple stroke points, the voltages at different positions are calculated by means of the characteristic equation, the duty cycle of every stroke point is regulated in real time, and the running speed of the motor is controlled. The experimental result shows that the error between the measurement speed and the calculated speed is less than 0.035m/s, the contact of vacuum circuit breaker can achieve the specified speed at the specified stroke point.