Although the implicit modeling is an important technique in 3D graphics, automatic algorithms to fit any given volumetric object by implicit skeletal elements are not very much advanced. Some automatic algorithms recently announced are very slow to take few days. we propose a fast algorithm to generate a set of metaballs to fit an arbitrary volume data by its isosurface. Experimental results for various input volumes show shorter generation time of within ten minutes on an ordinary worstation. A faster and robust rendering algorithm with no spots using Sturm sequence is also designed to render all the metaball images in this work, and it is 20? 30% (60% in some case) faster than that of using Bezier clipping.