Abstract: On the suggestion that a biped robot is equipped with heterogeneous legs of which one is bionic and the other is artificial, a mechanism scheme of multi-axis knee joint of the bionic leg is proposed, i.e., a four-bar linkage with instantaneous rotating center and bio-imitability. A dynamic model was thus established for the solution to inverse dynamic problem so as to obtain the control moments of knee joint for optimum gait patterns. Acquiring corresponding gait information by sensors, a moment control program was selected on computer, from which each and every gait pattern could be obtained by learning system. The bionic leg supported by MR damper responses rapidly and acts swiftly, especially is more symmetrical and harmonious than the gait of the artificial leg. The effectiveness of such a control has been proved by experiments.