1. A method for object positioning by using depth images, adapted to an object positioning apparatus, and the method being executed by a hardware processor to perform: converting a depth information of each of a plurality of pixels in each of one or more depth images into a real world coordinate; according to the real world coordinate, computing a distance of each of the plurality of pixels to an edge in each of a plurality of directions; assigning a weight to the distance of the each pixel to each edge of a plurality of edges; and according to a weight limit and the weight of the distance of each of the plurality of pixels to each of the plurality of edges, selecting one or more extremity positions of an object.