Abstract: Abstract: In order to study the influence of the end-effector's high speed contact with ground on the robot system when the hydraulically actuated multi-legged robot walks in a dynamic gait and realize its control as well, a single leg prototype of the bio-inspired hydraulically actuated multi-legged robot is developed. The robotic leg's structure is designed on the basis of research and analysis of the skeletons of the large dogs' hind limbs. The hip and knee cylinder layout are designed from the principle of rotating guide bar mechanism and swing guide bar mechanism, respectively. The torque of robotic leg's joint on stance phase is calculated on the basis of former biologists' research results and the planned joint trajectory of dynamic trotting gait on stance phase. The former biologists have already researched the dynamic gait of large dogs and separately measured the ground reaction forces on individual limb of trotting dogs using a series of four force platforms; the dynamic trotting gait trajectory with a speed of 2.5 m/s is planned as composite cycloid foot trajectory on flight phase with the same body height on stance. And the composite cycloid's foot trajectory is planned with the specifications: the stride length is 1 m, the stride height is 0.05 m, the period is 4 s, and the duty cycle is 50%. Based on the above bionic design, the mechanical parameters of the robotic single leg are determined: the length of thigh and shank is 0.35 m, the hip joint angle range is -50°, 70°, the knee joint angle range is -140°, -20°, the diameter of the cylinder piston is 0.02 m, the diameter of piston rod is 0.01 m, and the stroke length of the piston rod is 0.1 m. The virtual prototype of robotic single leg is designed via the three-dimensional modeling software Solidworks according to the design parameters. Furthermore, the feasibility of the parameters of the designed mechanical structure and hydraulic actuator is verified based on the dynamic vertical hopping simulation in MATLAB/Simulink. The dynamics of hydraulic single leg on flight phase and stance phase are formulated with the symbolic math toolbox of MATLAB, and the hydraulical single leg hopping control schemes on flight phase and on stance phase are designed, respectively. The conventional PID (proportion integration differentiation) controller is applied to control the angles of both joints at the desired angle values when the single leg is on flight phase; the cascade compliant control strategy is applied on stance phase. The initial condition of vertical hopping is that the single leg is dropped from the height of 0.65 m without vertical and horizontal velocity. The control parameter is set to make the single leg hop continuously to the desired height. The normal flow of the proportional servo valve with the differential pressure of 3.5 MPa is 0.67×10-3 m3/s. The dynamic hopping simulation experiment result shows that the single leg continuously hops to the height of 0.65 m, and the mean flow of hydraulic system is 5.6×10-5 m3/s when the hydraulic pressure is set to 16 MPa. At last the hydraulical single leg prototype is manufactured based on the virtual prototype of robotic single leg. It comprises the vertical hopping system with hydraulic power unit and the control system. The single legged vertical hopping experiment is successfully carried out on the hopping system. The single leg is able to hop continuously along the vertical guide rail when the parameters of conventional PID joint angle controller are set to reasonable values. The research of the paper provides the reference for the design of bionic multi-legged robot's single leg.