Abstract: In order to identify the proximity relations between the constraining objects,the characters of the constrained Delaunay triangulation which is built while contour lines are analyzed,elevation points and terrain variation lines are constrains,and a detailed classification for edges of the constrained Delaunay triangulation is made,a method for constructing one kind of hierarchical structure of the contour lines is proposed.The technologies on adjusting the direction of the contour line based on this hierarchical structure are studied.