Patients with complete paralysis that only walk with the assistance of exoskeleton robots because they lost their ability to walk. However, robots do not allow the exoskeleton robot to grasp the current state before walking and change the walking pattern. A "Stability Circle Region" was proposed to determine the current state of the exoskeleton robot. The Stability Circle is an area that can determine the possibility of a fall situation before the next walk using the link parameters of the robot and the current center of gravity of the patients. This study verified the validity of "stability circle" by simulating the change in the center of mass. Simulation results can be used to determine the stability of walking depending on whether the position of the center of mass before the walking is included in the circle area.