Aiming at the low efficiency and high labor cost of carton packing in express industry, the work studies the standard postal box of 350 mm×230 mm×190 mm and designs a kind of semi-automatic carton packing machine. The mechanical system of packaging machine was composed of a pallet rotary mechanism, an unfolding and shaping mechanism, and a hinge-bending mechanism to realize the carton packaging. The unfolding and shaping mechanism unfolded the carton gradually to a cuboid; the hinge-bending mechanism drove the short or long blades of the carton to turn 90 degrees; and the pallet rotary mechanism ensured the continuity between the processes in the packaging process. In conclusion, the packing machine can greatly improve the packaging efficiency and reduce the packaging cost on the premise of ensuring the packaging quality.