An optical detection system includes a marker product and an optical encoding device. The marker product includes a substrate and at least one structural portion. The structural portion has a first surface, a second surface and a dividing axis. The first surface and the second surface are arranged on opposite sides of the dividing axis. A sidelong direction aligning the first surface with the second surface is parallel to a moving direction between the optical encoding device and the marker product. The optical encoding device is disposed adjacent by the marker product. The optical encoding device includes an optical projector and an optical encoder. The optical projector is configured to project the optical detecting signal onto the marker product. The optical encoder is configured to receive an optical reflecting signal from the marker product and encode intensity variation of the optical reflecting signal into digital data.