In order to reduce the overall energy consumption of the hydraulic excavator, the potential energy recovery system of boom with closedcircuit of hydraulic excavator is proposed using to the energy storage equipment of hydraulic accumulator. 80 kN hydraulic excavator is selected as the study object. The torque balance equation of the shaft system of the motor-pump for energy recovery was established on the basis of the working principle of system, which showed that the average work pressure of accumulator is twice the load pressure of boom arm when the motor was not input power for the shaft system of motor-pump. The relation between the average accumulator work pressure and load pressure was analyzed in considering the torque balance equation of the shaft system of motor-pump. The results show that minimum and maximum work pressures are 16.04 MPa和19.56 MPa respectively for 8-ton hydraulic excavator according to the boom descending experiment under half load condition.