This paper presents a simple method to generate a gait tragectory of a compass type biped walking model. The method relies on the symmetric characteristics in the dynamics of the model. The motion genertated by this method resembles that of Passive Dynamic Walking phenomenon, as the motion consists of a free motion phase and an impact event taking place one after another. The two differs in the point that the method is constructed against a level surface, while Passive Dynamic Walking occurs on a shallow slope. The method will be introduced through a brief discussion on the dynamical property of the model, followed by a simulation example.