In order to carry out 3D visualization reconstruction of underground tunnel, this paper presents a new method based on sparse 3D scattered points. According to the shape of the underground tunnel, a three-dimension mathematic model of tunnels with trapezium section is built up. Dividing the tunnel into segments, according to the sparse 3D scattered points to get the central position, length data and the vertexes of the tunnel's each segment, we can draw every surface of each segment, so as to reconstruct the whole tunnel. As is proved by experiments, this method needs only a small amount of three-dimension points, and has noise immunity and stability.