In the pump controlled motor speed regulation system, due to resaons of pump and motor while working continuously of oil suction and discharge, and oil had compressibility, which make the system flow pulsation and pressure unstable, so the motor output shaft speed is produced of larger fluctuation, thus affecting the rotary workpiece machining quality. Through the motor shaft installation of an inertia plate, the work of system was made in advance for the inertia plate to absorb the flow pulsation. System flow fluctuation was reduced, pressure stability was improved, and the motor shaft speed fluctuations were reduced. After the experiment verified the feasibility of this method, it is shown that on the motor output shaft with inertia plate could reduce the system flow pulsation, and the motor shaft speed is more stable. In order to solve the flow pulsation in actual working condition of the impact on the motor speed, this conclusion provides a reliable method.