From the viewpoint of the system's mechanical energy, the passive inverted pendulum model (PIPM) is proposed for the generation of more energy-efficient biped gait pattern. The generated walking pattern, based on the PIPM, enables the fully actuated biped robots to closely mimic the behavior of stable passive walking, so that it can have good energy-efficiency, which is the inherent advantage of the passive system. Furthermore, the pattern generation method is extended to any desired terrain as well. As for SHR-1, the first-generation biped robot of Shanghai Jiao Tong University, gait synthesis is clarified in detail. Finally, the walking experiments are carried out on SHR-1, and the effectiveness of the proposed pattern generation method is confirmed.