The invention discloses an automatic board grinding mechanism. The automatic board grinding mechanism comprises a frame; the frame is provided with a rectangular groove; a board fixing and shifting module is arranged on the rectangular groove; the board fixing and shifting module comprises guide rail sets vertically arranged at four corners of the rectangular groove; a bearing table is horizontally connected among the guide rail sets; brackets are respectively arranged at four corners of the bearing table; square grooves are respectively formed in one adjacent corners of the four brackets; boards to be polished are placed among the four square grooves; a polishing module is arranged above the bearing table; the polishing module comprises support columns arranged at four corners of the frame; the top surfaces of the support columns are horizontally connected with a support plate; a cross guide rail is arranged on the bottom surface of the support plate, and comprises an X-directional guide rail and a Y-directional guide rail; a slide block is arranged at the bottom of the Y-directional guide rail; a rotating shaft is arranged at the bottom of the slide block; and a grinding disc ishorizontally arranged at the bottom of the rotating shaft. The automatic board grinding mechanism has such advantages as convenience in polishing, high safety and good polishing effect.