A drive mechanism for a scannerincludes a delivery device, a first rotational speed motor and a second rotational speed motor. The delivery device consists of an actuating wheel, a passive wheel and a conveyor belt. The conveyor belt is carried by the actuating wheel and the passive wheel, and the axes of the passive wheels are attached to two ends of the inner side diameter of the actuating wheel. The output shaft of the first rotational speed motor is provided with an actuating skew gear that engages two passive skew gears. The output shaft of the second rotational speed motor is also provided with an actuating skew gear that engages two passive skew gears. The drive mechanism uses the two motors to drive the two passive skew gears so as to better control the rotational speed and to scan the document image.