The purpose of this thesis is to develop a dynamic model of biped locomotion and implement a suitable controller for it . The locomotion aimed to be realized in this thesis is walking on a flat horizontal sueface in the sagittal plane. a planar five-link biped robot , which consists of a torso, two thighs and two shanks, with five degree of freedom is modeled. A gait cycle of the walking motion includes the single support phase(SSP), the impact phase and the support end exchange phase. The dynamic equation at SSP is derived by using the Lagrangian formulation and the impact equation is derivd by using the momention change caused by the nonconservative force during impact and the constraint imposed in the impact leg.