Abstract: In this paper,a new approach based on whole object is pursued to compute the binary topological relationship between unchanged contour line and changed contour line,in which FL points are introduced,intersection and difference operators are selected from set operators to distinguish the topological relations between neighboring spatial line objects;three types of topological invariants are used for the computational results of set operations: contents,dimension and connectivity-number.Then a computational method of contour line fusion is designed and realized.The proposed approach of contour line fusion is operational;it has been used in the automatization of contour line fusion successfully.