The invention provides an automatic screw locking device and a small screw chuck thereof. Gaps (5) and circumferential pin holes (6) are formed in the lower end part of a connecting piece (4) of the screw chuck (1); a conical open piece (7) is arranged on the lower surface of the connecting piece, wherein the conical open piece consists of a plurality of conical pieces (8); an arc-shaped convex piece (9) is arranged at the upper end of each conical piece; each arc-shaped convex piece (9) is also provided with a corresponding convex piece pin hole (10); a pin (11) is inserted into each circumferential pin hole and the corresponding convex piece pin hole (10); an elastic outer ring (12)is sleeved in a close fit manner; a vertical linear guide rail (21) and a sliding block (22) thereof, an automatic screwing tool (23), the screw chuck and an air cylinder (26) are arranged in front of a mounting plate (20) of the automatic screw locking device; a connecting rod (27) and a stressed spring (29) thereof are additionally arranged at the tail end of a piston rod of the air cylinder; the automatic screw locking device also comprises an automatic screw supply machine (30), wherein the screw outlet of the automatic screw supply machine (30) is connected to an inclined opening (3) of the screw chuck (1) through a screw conveying pipe (31), so that the automatic screw supply machine goes into the side of a reinforced wall in an unimpeded manner.