According to the effect of the human joints and the motion characteristics of the models’ footstep, combining with the distribution condition of degree of freedom of biped robots lower extremity structure in and abroad, we determine the number of the degree of freedom of robots legs is 12. Hip joint which has the characteristics of left and right axial rotation at horizontal direction, anteroposterior axis rotation and vertical axial rotation has 3 degrees of freedom. Ankle joint has 2 degrees of freedom which can rotate in left, right, pre and post directions is similar with the human ankle. Knee joint has a degree of joint and it extend the legs. The key of the design of humanoid robots is the joints design. The design of degrees of freedom of the joint is very important for whether the robots can walk successfully.