An optical tracking method disclosed in the present invention includes obtaining a continuous image set containing a reference light source during a period, and identifying an image characteristic variation of the continuous image set. The reference light source is set at a constant illuminated mode, and generates a known illumination variation during the period. The optical tracking method further includes comparing the image characteristic variation with the known illumination variation to determine whether a predetermined function is actuated. The predetermined function calculates position information of the reference light source on an image of the continuous image set.