Based on the driving structure, working principle and working condition of a parallel hydraulic hybrid system in an excavator, the parameter design and matching were studied.  Considering the installation, service life and the stableness of the engine, a method how to set the working pressure of the hydraulic accumulator was proposed. Then, to show the hybrid system’s greatest advantage at its working area and reduce the power of the enegine and the pump/motor, the parameter design of engine power and pump/motor displacement were studied. The matching results were analyzed using the built hydraulic hybrid excavator model based on AMEsim software. The results show that it can improve the distribution of engine’s working points and restrain the pressure of the hydraulic accumulator without sacrificing the stability of the engine. The energy saving of the hybrid system is at around 11.21%. The working pressure and rated volume of accumulator in different energysaving system are brought forward.