In the traditional hydraulic system with external active load condition, the cavitation phenomenon is produced easily,resulting in pressure fluctuations, runaway flow, cavitation and other phenomena.The independent metering system based on mechanical hydraulic pressure compensation was taken as the research object, and the hydraulic system schematic was simplified. In order to prevent cavitation phenomenon, the throttle characteristics of the metering in and metering out orifice were analyzed, and the minimum area ratio μ of metering in and metering out orifice was obtained. The simulation models of the independent metering system and load sensing system were built by using the simulation software AMESim, and the simulation analysis of the hydraulic cylinder extension and retraction working modes were carried out. The results show that in the load sensing system, the pressure of the inlet chamber falls below 0 with the increasing of the load F, which is called cavitation phenomenon; in the independent metering system, the inlet chamber pressure can be kept as the target pressure pm by changing the area ratio μ of metering in and metering out orifice, as a result that the cavitation phenomenon can be prevented.