For the purpose of solving the endurance problem in the process of unmanned aerial vehicle(UAV) line patrol, an autonomous line patrol system of UAV based on leapfrog charging is designed and implemented. As the first part, the autonomous positioning of UAV based on Global Positioning System/Real-time Kinematic (GPS/RTK) is studied in this paper. Firstly, aiming at the goal of UAV autonomous line patrol proposed by China Southern Power Grid Corporation, a leapfrog charging platform is built to improve the endurance of UAV. Then, in order to ensure that the UAV can conduct autonomous navigation according to the preset track and accurately land on the ground platform for charging, the key technologies of autonomous line patrol in the UAV GPS / RTK integrated navigation module are studied. Finally, the three main links of attitude calculation, acceleration compensation and delay compensation in line patrol technology are experimentally simulated. Experimental results show the attitude calculation algorithm can accurately estimate the flight attitude of UAV in flight and can quickly compensate the motion acceleration in time. The delay compensation algorithm can effectively solve the problem of positioning sensor delay. When the barometer output altitude data is unhealthy, the system can identify the health status of the data and automatically fuse the GPS output altitude data. Therefore, the methods and research conclusions proposed in this paper have important engineering guiding significance for the autonomous line patrol of UAV.