For the work characteristics of the volume adjustable hydraulic pump，its control and working principle in the hydraulic excavator were analyzed. And as a basis, the simulation model of a volume adjustable pump and a hydraulic excavator machine was established. The simulation results show that the discharge ratio of the volume adjustable pump is an important control parameter which can achieve a greater impact on the efficiency of a hydraulic pump. When the excavator is in the fine operation phase，a reducer is used to adjust the pump speed，and the increase of the discharge ratio can improve the efficiency of the pump，so the fuel consumption is decreased by 165% which improves the overall fuel efficiency.