Abstract: Enormous cross section data were generated in medicine，geography，aerodynamics， etc．After extracting the isolines of medical cross-section data set，we first link every two adjacent contours by triangular facets and then progressively fill the volume of each specific substance with tetrahedra to obtain the layered geometrical model for virtual surgery and scientific visualization．Our algorithm has the advantages of running fast，taking small space of storage，easy to control the shape of each tetrahedron and almost no need to insert new inner nodes．