Aiming at an excavator using tandem swash plate axial piston pump, the motion course with regulation characteristics of constant power was analyzed. A complete mathematical model of the closed loop control system was established, and Matlab/Simulink was used to simulate and analyze it, to get characteristic curve of the Load pressureOutput flow of the piston pump. A hydraulic test bench was built up to verify the effectiveness of the mathematic model. The effects were discussed with focus of power setting spring stiffness on the characteristics of constant power, and optimization measures were proposed for a threespring structure. The performance curve was obtained after improvement through simulation. After comparison it is found that the degree of fitting of constant power curve is significantly improved, by the way, provides a reliable theoretical basis for this type of study.