Aiming at the large-scale outdoor environment, a localization and navigation method based on 3D lidar is proposed, and a localization and navigation system for patrol robot based on 3D lidar is designed and completed. Firstly, the system records the patrol points and the environment 3D point cloud data traversed by the patrol robot in the remote-control mode. Then the recorded point cloud data is used to establish the environment global point cloud map, and the patrol path is planned according to the environment global map and patrol points. After obtaining the environment global map, the localization information of the robot is calculated by matching the current lidar scanning data with the global map. The experiments in outdoor large scene show that the navigation system can complete the perception of the inspection environment, map building, localization, and path planning, which can realize the high-precision trackless navigation of the robot, and ensure that the robot can accurately reach the designated patrol points to carry out patrol work.