WAVE is a bookshelf system that can freely expand or shrink according to space or user’s needs. The modular design system includes 7 basic elements: 5 cabinet plates of different sizes, and 2 metal rods, which enable freely combination with standard metal parts. With different cabinet board shapes, users could arrange the exact size or shape of the configuration they like with simple tools. With the change of the user's space angle, the bookshelf shape will also appear differently, making the ordinary wall a wavy water surface. This design has obtained a utility model design patent.