This paper focuses on the polygonal representation of a 3D object model which is composed of a lot of points on the object surface. In the 3D animation, it is sometimes necessary to use multi-resolution representation of a model to cope with various situations, and it is preferable to represent the models with different resolutions in a certain unified data structure. In order to meet theses requirements, this paper presents a new method which generates the approximated model of an original one by using multiple deformable models, called active balloon models (ABMs). We extract the three-dimensional skeleton of the object. The obtained skeleton comprises nodes and edges, and represents the structure of the object. Based on the skeleton, the approximated model is generated by deforming the ABMs. Some experimental works are made to verify the capability of our method.