According to the spatial posture characteristics of the urban road boundary, the method of automatically extracting road boundary point cloud and drawing road boundary lines was set up. Firstly, the spatial storage structure of the space grid point cloud was established, and used the normal vector feature of the whole point cloud in the grid to cluster and split them, and then the improved K-means algorithm was used to extract the road boundary point cloud. Finally, the road boundary line was drawn by the median method. Based on the method, the data of the straight section and the road segment scanning data of the experimental area are selected for analysis. The results show that the proposed method can extract the point cloud of straight line and curve line road boundary and draw the road boundary line without any auxiliary information, it has better extraction effect under the flat condition of the road.