1. A method for object positioning by using depth images, adapted to an apparatus for positioning an object, 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 a plurality of edges of the object in each of a plurality of directions around each of the plurality of pixels; 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 within a specified area range at least one pixel having a largest weight to determine one or more extremity positions of the object.