Abstract: Model simplification is used in a variety of disciplines, such as virtual reality, CAD/CAM, dynamic simulation and so forth. This paper presents a new method to delete vertex of the mesh model, which is based on volume criterion. To decide whether certain vertex can be removed, the method uses the variety value of volume when the vertex is removed as criterion. By the method, the simplified model can approximate original model very well. Because the volume criterion has distinct geometry and engineering meaning, the simplified model can be used as both displaying model and designing model. In order to improve the mesh quality, the paper introduces an optimal method based on swapping diagonal for re-triangulating the local mesh. The paper also gives an example to illustrate efficiency of the method.