The invention relates to a case body structure comprising an external packing case body assembled and positioned by a plurality of plates. The case body structure is characterized in that an external packing case body has predetermined wide plates with strong toughness formed by plastics, wherein bearing plates are erected at the bottom of the plates, a plurality of perforated protruding portions extends from the predetermined sections on the lower sides of the bearing plates to allow auxiliary plates for backing against the ground to be arranged among the protruding portions and allow fixing elements formed by plastics to be embedded to form a bearing set; connecting sections are concavely arranged on the joint sections of the wide plates erected by corners; and more than one through hole is arranged on plates of each erection section at the predetermined sections. Therefore, the plurality of plastic plates can be embedded via plastic fixing elements to be positioned into a whole when being assembled according to the width of an object. The inventive case body can replace wooden case, and can be randomly assembled and designed according to the specifications required by the object to be packed.