A power-driven spring booster for wheel chair is disclosed, which includes an electric motor, a transmission mechanism, a switch, and a buffer-driving structure, wherein the buffer-driving structure is installed on the transmission mechanism between the two wheels of the wheel chair, and the transmission mechanism is linked by power driving with the electric motor by means of the gear set, the chain-sprocket set, or the belt-pulley set, while a switch is disposed beside the arm rest of the wheel chair, by which to control whether the electric motor is activated or not. The buffer-driving structure can be a positive rotational spring and a negater spring. Thus, the transient impetus driven by the transient activation of the electric motor will not be directly transmitted to the wheel chair, but be absorbed by the buffer-driving structure, which then, after the action of wheel chair, gradually releases the elastic force to assist the wheel chair to move forward.
