Extensible 3D(X3D) is a software standard for defining interactive web and broadcast-based 3D content integrated with multimedia. The data size of Web3D representation based on polygon meshes is so large that transferring practical data fast is a hard problem. This paper proposes 3D object structure, a new framework for compact 3D representation with high quality surface shape. By utilizing a free form surface technique, qualified surface are transferred with limited amount of data size and rendered. 3D graphic structure can be regarded ad both polygon meshes and free form surfaces. Therefore, it can be easily integrated to existing Web3D data formats, for example VRML ＆ XML. 3D object structure also enables modeling free form surface shapes intuitively with polygon modeling like operations.