Unstacking method and unstacking system enables control device to accurately control a robot arm to take box of topmost stacking corresponding to target image according to two-dimensional image and three-dimensional image

An unstacking method comprises the steps of using a three-dimensional camera to photograph a stacking formed by stacking a plurality of boxes from the top to the bottom in order to obtain a two-dimensional image and a three-dimensional image; generating a processed two-dimensional image merely including the uppermost image of the stacking through the image processing device according to the depth information of the two-dimensional image and the three-dimensional image; intercepting two partial images with the same size as the template image but orthogonal to each other from the corners of the processed two-dimensional image through the image recognition device according to the upper surface image of the box taken as the template image; and comparing the similarity between the template image and the correspondingly two orthogonal partial images to find out a target image therefrom so that a control device can control a robot arm to pick up the topmost layer of the stacking and the box corresponding to the targ