Based on the practice of the 1000 kV AC transmission line project, experimental investigations of approach distance for live working on different working positions on 1000 kV AC transmission line were carried out. The research on minimum approach distance for live working on UHV (Ultra High Voltage) transmission line was based on the practice of Jindongnan Nanyang Jingmen (Jin-Nan-Jing) pilot project. The results indicate that it is safety and feasible to develop live working on 1000 kV AC transmission line in China. In this paper, switching overvoltage level and corresponding probability density of live working on the first AC UHV transmission line in China was analyzed; the calculation and correction method of live working risk was discussed; and the switching impulse discharge performances of live working electric structure on outer phase, middle phase and tension string on 1000 kV AC transmission line were studied. Based on the results, by calculation and analysis of the risk, the minimum approach distance for live working was determined. The results of this experimental investigation provide technical support and are available for reference to perform live working on 1000 kV AC transmission line.