A modular panel-packing box receives a plurality of panels, and includes a base, two partitioning units, a loop-shaped surrounding wall, and a top cover. Each of the partitioning units includes a socket and at least one partitioning member. Any two adjacent ones of the base, the socket, the partitioning member, the surrounding wall, and the top cover are interconnected removably. Each of the base, the socket, the partitioning member, and the top cover is folded, and is unfoldable to form a flat plate for facilitating transportation and storage of the modular panel-packing box.