Packing box is a modular building product based on steel frame and lightweight wallboard structure system. The product is composed of top frame, bottom frame, corner post and 14 interchangeable wallboards, which can be packaged for land or sea transportation. The circuit is pre-installed in the top frame and the wallboard, the drainage pipe is pre-installed in the bottom frame, and the doors and windows are pre-installed in the wallboard, which can greatly reduce the construction period on the site. Usually 4 workers can complete the installation of a single box in 3 hours.