This paper presents a computational model for a nonlinear two degree-of-freedom (2-DoF) robotic leg. The model is based on a mathematical model of two connected body segments to mimic the lower thigh and shank of human leg. Two sets of electro-hydraulic servo systems (EHSS) are seperately used to drive the robotic thigh and shank. The dynamic of EHSS is accurately developed to exhibit the relationship of the input current and the actuated force\torque. A velocity observer is used to estimate the angular velocities of the robotic thigh and shank. Then, a velocity feedback controller is proposed to track the hip and knee joints movements of robotic leg. The simulation results show that the velocity feedback controller gives better tracking performances in term of position control strategy when compared with the conventional PID controller.