A new technology used in expanding machine was introduced which was how to use servo motor drive and control hydraulic pump. Metering pump was driven by servo motor as power source, and rotation rate and torque of servo motor could be changed by control unit so as to achieve compound control to flow and pressure. This power source can not only simplify the structure of hydraulic system, but also save energy and reduce noise. It’s a trend in the development of hydraulic power source in the future.