To realize the dynamic running of quadruped robots, a bio-inspired hopping leg prototype based on hydraulic actuation is developed. Firstly, the DOF (degree of freedom) configuration of a robot leg is discussed according to the anatomic analysis of quadruped mammals. Secondly, the trotting simulation on flat terrain is carried out to obtain the torque output characteristics of joints. Thirdly, the hydraulic actuators, joint driver mechanism and the 4DOF leg prototype are designed based on the analysis of simulation results, as well as the control system. At last, the test bench for the leg prototype is constructed to test the performance of the leg in vertical hopping experiments, in which the validity of the mechanical and control system design and the algorithms are verified.