The utility model relates to the technical field of battery packs. The box body structure comprises an upper cover, base plate and frame, the upper cover, the bottom plate and the frame are connectedto form a closed space; wherein the frame comprises fixing ribs and borders, the fixing ribs and the borders are connected to form a latticed frame, the borders and the bottom plate are welded, the bottom plate sequentially comprises an inner-layer plate, a connecting part and an outer-layer plate from top to bottom, bolts penetrate through the fixing ribs and the inner-layer plate and are connected with the connecting part, and the connecting part is fixedly connected to the outer-layer plate. The plates are connected and fixed through the connecting pieces, the structural strength of the boxbody is improved, and the air tightness problem of the bottom plate caused by welding in the bottom plate manufacturing process is reduced.