Abstract: The dynamic model of biped robot is built with Lagrangian method. When two feet stand on the ground, restriction of kinematic equation brings redundance of degrees of freedom to biped robot. This paper uses Lagrangian coefficient to eliminate the redundant degrees of freedom of the biped robot. Trajectory tracking of biped robot is controlled by robust control method. Simulation result proves that robust control method can effectively restrain the effect of imprecise model or external disturbance acting on biped robot, and the trajectory tracking control on biped robot is effective.