Abstract: A new leg mechanism with 7 DOF(degrees of freedom) and double spherical hip joint is proposed in this paper.Comparing with traditional 6 DOF biped mechanisms,it has the following two advantages.First,the double spherical joint can realize the basic function of waist motion without waist joint,enabling the humanoid robot to walk erectly.Secondly,if positions of the foot and waist are given,it can rotate the legs in a manner similar to human.This paper also discusses such problems of this complex mechanism as motion characteristic analysis,kinematics solution,motion planning,and validation experiments.