To ensure the safety of vehicles on the bridge and ships under the bridge at the same time, lidar can be used to monitor the vehicle flow on the bridge and calculate the passing time; to monitor the speed and height of ships under the bridge, calculate the passing time and make corresponding countermeasures. Lidar can better meet the requirements of scanning and monitoring objects on the bridge and under the bridge. If there are foreign matters in the monitoring area, it can timely alarm and reduce accidents.