Generally, it is necessary to determine the pressure level of the system first, and then preliminarily determine the displacement of the motor according to the load to be borne. The torque formula of hydraulic motor is T=(pv* mechanical efficiency) /(2*3. 14). The practical significance of motor torque is the ability to drive a rotating load. As the driving source of the system, the motor should be calculated from the load and finally determined. How much torque and speed the actuator needs, then calculate the transmission mechanism and finally determine the specifications of the motor. The shell pressure and oil return pressure of the motor are required. Generally speaking, the return oil pressure is greater than the shell pressure, so the plunger will touch the stator ring. If the housing pressure is greater than the oil return pressure, the plunger will be pushed away from the stator ring. When the oil return port is switched to the high pressure port, the high pressure will impact the plunger on the stator ring, resulting in knocking sound, which will cause large and small pits on the stator ring for a long time and make the motor fail quickly.