Biped robot has attracted increasing attention because of its flexible movement and strong adaptability to the surroundings. However, the small output torque and the weak impact resistance of motor drive, as well as the large energy consumption of hydraulic drive limit the performance of biped robot drive system. Aiming at these shortcomings, an electric-hydraulic hybrid drive system of biped robot was proposed in this paper. The robot platform was designed based on the prototype of Zhejiang Lab biped robot. The mathematical model of hydraulic drive system and the simulation model of mechanical structure were established to analyze the dynamic characteristic and the load force during walking. The value function reflecting the energy consumption of the hydraulic drive system was proposed. The pressure of the accumulator in the hydraulic power unit was selected as the control parameter. In order to get the minimum value of the value function, so as to reduce the energy consumption of the hydraulic driving system, the control parameters were optimized by genetic algorithm. From the simulation results, the proposed optimization algorithm can improve the efficiency by 3.49%.