Abstract: In view of the request of 3D visualization on tunnel in underground，according to the topology structure of tunnels and the raw data of tunnels，a 3D reconstruction algorithm on irregular cross section tunnel based on discrete points was proposed.In this algorithm，a collaboration strategy of the shortest diagonal line and adjacent contour is adopted，which can effectively approach to the real tunnel entities.The simulation detection shows that this algorithm is stable in performance，and can effectively realize the 3D fast reconstruction of irregular cross section of underground tunnel.

Key words: Discrete Points, Irregular, Tunnel, Three dimension