A new kind of walking assistance mechanism in aided-walking wheelchair is proposed to help stroke and cord injury patients on gait rehabilitation training and aided-walking indoor and outdoor. Each side of the walking assistance mechanism, which is a double-crank linkage mechanism actuated by one driver, assists the motion of thigh and shank synchronously. The mechanism can control the walking gait of both legs to assist the patients in walking and gait rehabilitation training. The mechanism is analyzed, and the optimal proportion of the structure dimension suitable for different person is obtained according to the clinical gait analysis data. The simulation results show that the walking assistance mechanism can simulate the nature gait during human walking and realize the walking assistance and gait rehabilitation training function.