For deep application of Lidar to patrolling electric power transmission lines, mathematical models are set up to calculate some important parameters in the task, including inclination of electric power transmission towers, bending of power lines, distance between crossing lines, safe space check around lines and so on. The problem that internal data process of Lidar system heavily depends on special commercial software is solved to some extent. All the models are tested with practically measured 3D Lidar point cloud and their fitness is proved, which helps to promote the advantages and effectiveness of Lidar in patrolling power lines.