A method of synchronization adjustment is applied to an optical detecting device, so as to synchronize an exposure timing sequence of an image detector with a light emitting timing sequence of an indicating light source. The method includes acquiring a continued image set, analyzing intensity of each image of the continued image set, and adjusting the exposure timing sequence according to duty cycle of the image detector and intensity ratio of at least two images. An exposure frequency of the image detector is greater than a flickering frequency of the indicating light source.