Abstract: In this paper, the global stability for fixed point of semi-passive biped robot walking is studied. The compass liked biped robot is powered by applying an impulsive push along the stance leg just before the heel strikes. The fixed point and its global stability of semi-passive biped robot walking are discussed based on Poincaré map. The inter-leg angle at heel-strike is always a constant by introducing a stopper. The existence of a fixed point and its global stability are proved for the semi-passive biped robot walking. The dynamical additional conditions for the existence of a fixed point are discussed. The simulation results show that the proposed semi-passive biped robot powered by applying an impulsive push, and introducing a stopper to keep a constant inter-leg angle at heel-strike can walk stably, and the fixed point is robust to various disturbances.