Abstract: Intra3D is an interactive 3D toolkit based on OpenGL. Its C++ class library and COM library integrates scene data structure, graphical objects, 3D interaction algorithms and graphical user interface. The architecture design and 3D interaction of intra3D reusable library are discussed in this paper. The library is composed of four layers: ‘basic objects and functions’, ‘graphical objects’, ‘scene graph and nodes’ and ‘rendering and interaction’. The design of 3D interaction is focused on ‘scene node transformation’, ‘mouse trackball algorithm’ and ‘3D user interface’.