Abstract: Contour tree is an effective method to express the spatial relations of contour lines. The adjacent relationship and inclusion relationship of contour lines can be expressed clearly by contour tree. Contour tree facilitates the processing of contour lines. This work studies how to construct contour tree by using of Delaunay triangulation, proposes a new method of generating contour tree. It fully uses the advantages of Delaunay triangulation in Domain Analysis, determines the spatial relationship of contour lines by using Delaunay triangulation twice, then unifies these contour lines which are truncated by figure profile to achieve the purpose of generating contour tree. In this work contour lines are used as a constraint edge to build a constrained Delaunay triangulation. Contour lines with neighboring relations are found by using of Delaunay triangulation. On this basis, the truncated contour lines are ascertained, identified and unified ultimately through combining the elevation of their neighboring contour lines. Then the two contour lines with neighboring relations are found again after the contour lines reunification by using of Delaunay triangulation. By using the elevation of the two contour lines to judge whether they are brothers or father-son relationship. The contour lines are inserted into the appropriate position in tree according to the relationship. And the contour tree grows gradually. This paper also gives algorithm design of the method of generating contour tree based on Delaunay Triangulation and experimental results.