The invention discloses a stay wire downward-pulling device comprising a main sleeve, a lead screw and a stay wire pin sleeve. One end of the lead screw is connected with a stay wire rod, and the other end of the lead screw is connected with the main sleeve. An opening allowing for introducing of a steel stranded wire is formed in the other end of the main sleeve. The stay wire pin sleeve is arranged in the main sleeve and in a round ball shape. A through hole is formed in the non-diameter position of the stay wire pin sleeve. The steel stranded wire is inserted into the through hole and fixed to the stay wire pin sleeve. An outer thread arranged outside the lead screw is engaged with an inner thread of the main sleeve. The diameter of the stay wire pin sleeve is 10 mm larger than that of the opening, allowing for introducing of the steel stranded wire, of the main sleeve. The main sleeve, the lead screw and the stay wire pin sleeve are all made of aluminum alloys. As a whole, the stay wire downward-pulling device has the advantages of being simple and convenient in mounting, firm in fixing, high in safety and easy to adjust, recycling can be achieved, and waste is reduced.