A method for dynamically learning a material of a working surface on which an optical navigation device is moving, includes: using light emitting unit (s) to emit light ray (s) to the surface so as to generate image(s) on an image sensor; estimating and calculating average offset(s) of image(s) of sensing pixel(s) of the image sensor according to at least one image motion information sensed by the sensing pixel(s) during a specific time; and, dynamically determining whether the image value(s) sensed by the sensing pixel (s) correspond to a fixed pattern or correspond to a feature image of the device moving on the surface according to the average offset(s) and a threshold.