The invention discloses an automatic carton distributing device. The device comprises a base, two roller brackets are symmetrically and fixedly mounted at the top end of the base, a conveying mechanism is rotatably mounted between the opposite inner walls of the two roller brackets, and a straight plate is fixedly mounted at the end, away from the base, of a supporting plate. A transverse moving mechanism is mounted at the top end of the straight plate, a lifting mechanism is mounted in the straight plate, an inclined sliding plate is fixedly mounted on the outer wall of one of the roller brackets, and two second motors are symmetrically and fixedly mounted at the top end of the base. The automatic carton distributing device is provided with the conveying mechanism so that cartons can be conveyed. The non-qualified cartons are clamped and lifted to be away from an output mechanism through the lifting mechanism, then the non-qualified cartons are put on the inclined sliding plate to becollected to a waste collection area in a concentrated mode, manual sorting is not needed, time is saved, and the distribution efficiency is greatly improved. Meanwhile, manual sorting and carrying are not needed in the distribution process, and labor force is greatly saved.