This paper presents a novel gait generation method of quasi-passive dynamic walking, achieving synchronous resonant gaits on level ground. This method utilizes the rotor as a driving force source, enabling flexible force forms. By introducing a rectified sinusoidal oscillation term to compensate the driving force, it mitigates gait bifurcations across multiple periods while improving locomotion energy efficiency. We propose a step-to-step frequency tuning method that achieves resonance locking between oscillation and gait frequencies without requiring complex model identification. Furthermore, stability of the synchronous resonant gait is analyzed by the Poincaré map. The proposed approach provides a solution for energy-efficient bipedal locomotion, enabling efficient walking gaits with simplified control and easily implementable actuation systems.