In order to improve the application performance of the hydraulic diaphragm metering pump, it is very important to select the proper crank rotating speed range. The whole simulation model of the hydraulic diaphragm metering pump is built through the AMESim platform. The spline curves of the open volume of the pump valve and the crank angle under different rotating speed were drawn, and then the lag angle of the suction and discharge valve was gotten. By calculating the volume loss rate caused by the lag of pump valve, the volumetric efficiency of hydraulic diaphragm metering pump at different rotational speed was obtained. According to the volume efficiency change rule, selecting the optimizing crank rotating speed range, thus this way provides a basis for the design and research of the hydraulic diaphragm metering pump.