The invention relates to a device and method for adjusting the size of a top die system hanging rack. The device for adjusting the top die system hanging rack comprise a vertical face protecting net frame, a movable plate, guide angle steel, first guide channel steel and second guide channel steel. The lower end of the vertical face protecting net frame is vertically and fixedly connected with the left end of the movable plate, and the left end and the right end of the lower surface of the movable plate are respectively provided with a plurality of vertical bearings and horizontal bearings. The guide angle steel and the first guide channel steel are arranged at the left end and the right end of a bottom plate of the hanging rack respectively. The second guide channel steel is arranged at the upper end of a vertical rod of the hanging rack. The left end and the right end of the movable plate are placed in an opening of the guide angle steel and an opening of the first guide channel steel respectively. The upper end of the vertical protecting net frame is placed in an opening of the second guide channel steel. According to the device and method for adjusting the size of the top die system hanging rack, the vertical face protecting net frame and the movable plate can slide along the guide angle steel and the first guide channel steel, so that the size of a rack body of the hanging rack is adjusted freely, and the hanging rack can be adapted to the size variation of a building core tube.