Incremental contour fusion plays a very important role in updating topographic database. The most popular fusion methods in current use depend on manual work basically, in which it results in large workload, low efficiency and it can't ensure the quality of the spatial data. Therefore, the automatization of contour fusion should be developed exactly. Topological relation between unchanged contour and changed one is an important topic for contour fusion. In this paper, a new approach based on whole object is pursued to compute the binary topological relationship between them, 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 14 fusion rules are concluded and a prototype system for automated fusion is implemented. The proposed approach is examined to be reasonable and practicable by real and simulated experimental data.