The invention discloses an automatic box conveying mechanism used for a machining machine. The automatic box conveying mechanism comprises a machine table, a box conveying mechanism body and a box changing mechanism. The machine table comprises a rack and a driving assembly. The driving assembly comprises an air cylinder and a first sliding seat. The first sliding seat is provided with a box conveying slope and a box changing slope. The box conveying mechanism body comprises a platform, a box conveying wheel and a tongue plate. The tongue plate bears the bottom of the platform and protrudes to the bottom of the platform. The box changing mechanism comprises a box changing wheel, a position guide block and multiple buckling pieces, and buckling piece positions are located above the platform. A box comprises a first box body located on the platform and second box bodies positioned on the buckling pieces. The air cylinder drives the first sliding seat to move so that the box conveying wheel can climb to the box conveying slope. The tongue plate is driven by the box conveying wheel to be disengaged from the bottom of the platform so that the first box body can get away from the platform. The box changing wheel climbs to the box changing slope and drives the buckling pieces so that the second box bodies can get rid of positioning from the buckling pieces to fall onto the platform. Thus, the purpose of automatically changing and conveying the box bodies is achieved, labor and working hours are reduced, and the production efficiency is improved.