Abstract: The realization of collaborative viewing and markup for 2D and 3D model of products is important in the net-based collaborative design. Aiming at the limitation of common markup software, the architecture of the collaborative viewing and markup system is constructed, and the function description of this system is presented. Finally, the system is implemented by VRML, OpenGL and Socket technology, and an application example is given. This system is an effective tool, enable geographically the dispersed designers to communicate based on product model in a net-based environment.