The invention discloses an external wall cantilever scaffold profile steel hole protection brick device and a construction method. When a brick wall is built, a U-shaped protection brick is installed in a cantilever profile steel position; a wall body around a hole and a heat preservation layer are effectively protected when the brick wall is built and cantilever profile steel is disassembled; and after the cantilever profile steel is disassembled, a protection brick cover plate and the U-shaped protection brick are fastened through bolts. Hole concrete pouring and blocking are conducted and completed indoors. The technology and the device are used for conducting hole blocking quickly and effectively.