Pendulum principle: When the patient's center of gravity shifts, the interactive chain (the center of rotation of the chain) device installed on the inner side of the thigh orthotic device achieves passive forward and backward movement of the switching limbs. For example, when the patient wears the orthotic device and walks, when the patient's torso tilts inward to one side, the other lower limb is driven off the ground, and then the center of gravity shifts, causing the lower limb of the mind to move forward by the interactive chain device under the action of gravity, and swing forward under the action of inertia to complete the action of stepping out the leg. The other principle is the same, completing the action of alternating steps.