A prototype of hydraulically powered quadruped robot is presented.The aim of the research is to develop a versatile robot platform which could travel fleetly in outdoor terrain with long time of endurance and high load carrying ability.The current version is 1.1m long and 0.48 m wide,and weights about 150 kg.Each leg has four rotational joints driven by hydraulic cylinders and one passive translational joint with spring.The torso carries the control system and the power system.A novel control algorithm is developed based on a Spring-Loaded Inverted Pendulum model and the principle of joint function separation.The robot can not only cross a 150 mm high obstacle in static gait and trot at 2.5km/h and lkm/h on the level-ground and 10°sloped-terrain respectively,but also automatically keep balanced under lateral disturbance.In this paper,the mechanical structure and control systems are also discussed.Simulations and experiments are carried out to validate the design and algorithms.