An optical trace detecting module is disposed in a computer input device. The computer input device is able to displace on a plane relatively, and has a light-pervious plate used for an object to contact with and move on a surface thereof. The optical trace detecting module includes a circuit board, a first projection set, a second projection set, and at least one optical path diverting element. An optical sensor is electrically disposed on the circuit board. The first projection set is opposite to the light-pervious plate. The second projection set is opposite to the plane. The optical path diverting element is disposed between the two projection sets and the optical sensor, so as to direct the sensing beams emitted by the two projection sets to reach the optical sensor, thereby generating corresponding control signals.