The cognition of human walking mechanism is an important foundation for the development of bipedal robots. During human walking, the external force moment is the decisive factor affecting the stability of walking, the interaction between gait and external force moment is a key issue in the study of human walking mechanism. The centroid angular momentum can reflect the change of external force received by the human body, but it will show different changing rules with the evolution of gait. In this paper, the human walking gait is taken as the research goal to accurately obtain the change of the real-time motion information and the centroid angular momentum during the human walking, Then, the mechanical analysis of the human gait is carried out according to the external force moment and the angle of centroid angular momentum during human walking, and combining with the changing rules between the foot-land relationship and the sagittal-centered centroid momentum during human walking, the conclusion is obtained that the angular momentum feature points and the gait feature points are highly consistent in time. Finally, the precise division of the human gait cycle phase based on the sagittal plane centroid angular momentum is realized. The result is of great significance for understanding the mechanism of human walking and guiding the rehabilitation therapy and the development of bipedal robot.