A sealing structure includes a box body and a cover body. The box body includes a plurality of side walls respectively including a plurality of outer and inner portions, an annular groove formed on the inner portions, and an annular protrusion portion. Each outer portion has a level difference with the corresponding inner portion. Any two adjacent ones of the side walls form a corner portion. An outer surface of each corner portion forms a sharp corner. The annular groove is arc-shaped at a position corresponding to each corner portion. Each corner portion includes a hollowed-out area. The cover body includes a main body in a polygonal shape with sharp corners, an annular protrusion portion protruding from the main body, and an annular groove. The annular protrusion portions extend into the annular grooves, so that the cover body is sealedly joined to the box body.