Abstract: This paper presents a method for boundary extraction of building roof from LiDAR point cloud.Firstly,a TIN model of discrete building roof LiDAR point cloud is built.Based on spatial geometry relationship in the TIN model,after some triangles with too larger side lengths than the average point distance are deleted,the borderlines of residual irregular triangulated network can be extracted to obtain initial boundary points.From the initial boundary points,points which two vectors have distinct change of slope are filtered as inflexion points.Some LiDAR points might locate outside the polygon constructed by inflexion points.So the inflexion points need to be expanded using all building roof LiDAR points.The final building roof boundary is constructed by the expanded points.The experimental result shows that this method is able to effectively extract all kinds of polygon building roof boundary.