A fast slicing algorithm for triangular mesh model was proposed. The node splitting algorithm and the clustering algorithm of R*-tree were improved and the spacial index structure of triangular mesh model was established based on the improved R*-tree. The position of slice planes was computed according to data nodes- distributing of the spacial index structure, thus the distribution of slice planes was intensive in the cragged region of triangular mesh, and the distribution of slice planes was sparse in the smooth region of triangular mesh. The intersection triangular facets with slice plane were obtained with depth-first traversal algorithm of R*-tree. The intersection line segments between slice plane and interection triangular facets were computed and they were sorted end to end, then the orderly section contour lines were obtained. It was proved that this algorithm can obtain section contour line accurately, effectively and has strong adaptability of triangular mesh model.