The method for fitting a sheath on a cable harness includes a series of steps including determining the length of sheath to be used, mounting the sheath on a mounting tool of tubular shape, inserting the cable harness into the mounting tool, removing the mounting tool and arranging the sheath around the cable harness, fitting a sheath stop at one of the ends of the sheath, the sheath stop fastening the end of the sheath to the cable harness stretching the sheath over the cable harness so as to extend it and tension it, and fitting a sheath stop at the other one of the ends of the sheath.