Abstract: Based on the Delaunay triangulation method, this paper presents an automatic triangular mesh generation algorithm for arbitrarily shaped planar regions. This algorithm has the advantages of adaptation to complicate boundaries, high quality boundary mesh and full automation. Approaches such as topological refinement and smoothing are incorporated. The algorithm has been realized through redeveloping autoCAD by ARX. Great many examples are included to demonstrate the reliability and practicability of the algorithm.