The invention relates to a demounting and mounting device of a sling or a strengthening steel wire rope for a steel safety shell and a use method. The demounting and mounting device comprises a firstpulley mechanism fixed to the ground surface at the position of a lower opening of a cylinder ring or a lower opening buttress, and a second pulley mechanism fixed to the position of a connecting mechanism at an upper opening of the cylinder ring or the position of a lifting lug. A lifting steel wire rope is connected between the first pulley mechanism and the second pulley mechanism in a surrounding manner. One end of the lifting steel wire rope is connected with the lifting device, and the other end of the lifting steel wire rope winds around the first pulley mechanism and the second pulleymechanism and is used for being connected with the sling or strengthening steel wire rope to be mounted or demounted. By means of the demounting and mounting device and the use method, the structure is simple, the cost is low, use is convenient, and safety is high.