Abstract: In practice, property information such as colors, textures, surface normals, etc. is necessary to represent 3D models besides geometry and topology information of triangle meshes, which will inevitably result in a large volume of 3D data as well as boundary edges and holes of mesh models. In order to decrease the data volume as well as preserve significant character of 3D models, an improved quadric error metrics and error control method were used to present a new simplification algorithm of unclosed mesh models based on triangle collapse. With the conception of geometry and property boundary, the original meshes were labeled as boundary, corner, interior or character triangles according to different boundary conditions, and constraint strategies were adopted to preserve appearance and boundary of the original models during the simplification process. In addition, a method to generate progressive meshes was given to provide a continuous multi-resolution representation of 3D models. The proposed method has been successfully applied to progressive transmission and presentation system of 3D models over the Internet.