1. A method of synchronization adjustment applied to an optical detecting device for synchronizing an exposure timing sequence of an image detector with a light emitting timing sequence of an indicating light source, the method comprising: acquiring a continued image set; analyzing intensity of each image of the continued image set; adjusting the exposure timing sequence according to intensity ratio of at least two images and a duty cycle of the image detector; comparing intensity of at least parts of pixels of each image to a threshold; determining whether the image detector captures the indicating light source according to a comparison; increasing an exposure frequency of the image detector when the image detector captures the indicating light source; executing the synchronization adjustment of the exposure timing sequence and the light emitting timing sequence; and decreasing the exposure frequency of the image detector when the exposure timing sequence and the light emitting timing sequence are in synchronization; wherein the exposure frequency of the image detector is substantially greater than a flickering frequency of the indicating light source.