Abstract: A quasi-passive energy storage design and analysis of the lower extremity exoskeleton was proposed to alleviate the burden of the key bearing joints and assist walking. In combination with the gait law of the human body, the method of series elastic energy storage components was adopted to accomplish energy storage in the process of passive follow-up human body movement, thereby achieving the purpose of saving energy consumption of the human body. According to the change of the hip and knee joint in the normal gait, the corresponding hip joint adaptive system and the knee joint variable stiffness system were designed, and the smooth switching between the support state and the swing state of the lower extremity exoskeleton was achieved based on the three-state energy control strategy. In the end, walking assistance was obtained without hindering the normal walking of the human body.