The invention relates to the technical field of packaging, and discloses an automatic carton opening device for carton packaging. The automatic carton opening device comprises a shell, wherein a button is fixedly connected to the outer part of the shell, a handle is fixedly connected to the outer part of the shell, a shearing opening is formed in the surface of the shell, a first gear is fixedly connected to the inner part of the shell, a connecting plate is fixedly connected to the outer part of the first gear, and a connecting rod I is movably connected outside the connecting plate. Under the interaction of the shearing opening, the first gear, the connecting plate, a first connecting rod, a second gear, a second connecting rod, a sliding rail, a first detection assembly, a sliding block, a feeler lever, a supporting plate, a U-shaped magnetic plate, an electromagnet, a rotating shaft, a cutting blade and a baffle, the depth of a cutter for people to open a carton package and cut into a carton can be easily controlled, the situation that packaged commodities are damaged due to the fact that the cutter is inserted into the carton too deeply is avoided, the problem that hands are scratched when the cutter is used for opening the package is effectively solved, and the carton package opening process is safer and more efficient.