The two main parameters of mud pump performance are displacement and pressure. The displacement is calculated by discharging several litres per minute. It is related to the diameter of the borehole and the required speed of the flushing fluid from the bottom of the hole. That is to say, the larger the diameter of the hole, the larger the displacement required. It is required that the upward and backward velocity of the flushing fluid can flush the cuttings and rock powder from the drill bit off the bottom of the hole in time and carry them to the surface reliably. When drilling for geological cores, the upward and backward velocities are generally about 0.4-1 m/min. The pressure of the pump depends on the depth of the borehole, the resistance of the passage through which the flushing fluid passes and the nature of the flushing fluid transported. The deeper the borehole is, the greater the resistance of the pipeline and the higher the pressure required. With the change of borehole diameter and depth, the displacement of pump is required to be adjusted at any time. The pump mechanism is equipped with a gearbox or a hydraulic motor to adjust its speed in order to achieve the purpose of changing displacement. In order to accurately grasp the changes of pump pressure and displacement, flowmeters and pressure gauges should be installed on mud pumps to keep drillers informed of pump operation at any time. At the same time, pressure changes can be used to judge whether the condition in the hole is normal or not in order to prevent accidents in the hole.