The invention discloses a building wall polishing machine capable of quickly replacing a polishing disc. The machine comprises a dustproof cover; a mounting plate is arranged in the dustproof cover, and is fixedly connected to the inner side wall of the dustproof cover; a motor is fixedly mounted on the mounting plate; the tail end of an output shaft of the motor penetrates through the mounting plate, and is fixedly connected with a rotating shaft; the end, far from the motor, of the rotating shaft is detachably connected with the polishing disc; a connecting head is arranged at the middle part of the polishing disc; a mounting groove is inserted in the connecting head; two limiting blocks are symmetrically arranged in the mounting groove; two guide rods are arranged in the mounting groove, and are respectively positioned on two sides of the mounting groove; and two ends of the guide rods are fixedly connected to two opposite side walls of the mounting groove. The machine is simple instructure and convenient to operate, can convert an angle to easily finish the polishing operation on a top wall, is excellent in polishing effect, can quickly replace the polishing disc, improves theworking efficiency, and deserves popularization.