The invention relates to the technical field of polishing, in particular to a plate polishing device for manufacturing of an electric fire box. A rail plate is fixedly connected to the inner side of aworking frame, a second sliding groove, a placing groove and a first sliding groove are formed in the inner side of the rail plate from inside to outside in sequence, electric wheels are slidably connected to the inner side walls of the first sliding groove and second sliding groove respectively, and connecting rods are rotatably connected to the inner sides of the two electric wheels through rotating shafts respectively; an electric retractable rod is fixedly connected to the inner sides of the two connecting rods, the bottom of the electric retractable rod is fixedly connected with a polishing machine, a base is fixedly connected to the inner side of the bottom of the working frame, casing pipes are fixedly connected to the left and right ends of the base respectively, and sleeve rods are slidably connected to the inner sides of the casing pipes. Through arrangement of the electric wheels, the connecting rods and the sliding grooves, polishing of a whole wooden plate is completed automatically, the process is simple, the operation is stable, the working efficiency of the device is greatly improved, and meanwhile the labor cost is reduced.