Abstract: The DTM surface construction of the open-pit mine was completed under the Auto CAD platform，and the surface model and the secondary boundary model were constructed based on the wire⁃ frame model by using the triangulation algorithm，and their intersection lines were obtained. Based on the intersection line shear surface and the secondary boundary line frame model，the final boundary line frame model with terrain line is formed，the establishment of three-dimensional visualization model is realized， Build application menus，compile application programs，and finally realize the programming of DTM sur⁃ face construction and operation in the finel realm of open-pit mines. It is of great significance to improve the accuracy and efficiency of design while reducing the error for drawing the final boundary design map of open-pit mines.

Key words: Auto CAD secondary development, open-pit boundary design, DTM surface construc? tion, Delaunay triangulation algorithm