Abstract: A new method is presented for removing the shortages of the Cuberille method which has lower precision and poor image quality. Iso-surface（cube sides） produced by the Cuberille method is taken as a framework,and is covered with a polygon grid. The polygon grid is produced by expending the cube sides with a linear interpolation. This expansion improves the precision of the Cuberille method,and makes the polygon grid have linear precision. How to determine the position and normal at each polygon vertex and how to construct the polygon grid are discussed. The polygon grid produced with new method has clear geometric meaning. The normal vectors computed with new method are compared with those produced with Marching cube method. The result shows that the smoothness of the image is obviously improved. Finally,the complexity of the new method is discussed,and using an instance the Cuberille method and Marching cube method are compared on the effect and time consumption.