Experimental study on safety distance of live working is carried out in high-altitude areas for 220 kV transmission line in order to supply technical base for live overhaul and maintenance of 220 kV line and guarantee safe operation of live working. Switching impulse discharge characteristics tests of live working in different working positions of trim-size tower for 220 kV transmission line are performed in Yangbajing, Tibet (4300 m), Wulan, Qinghai (3000 m), Xiaowan, Qinghai (2200 m) respectively. The discharge characteristic curves under different work conditions are given. According to the above test results and the existing research on low altitude areas for 220 kV transmission line live working, the required live working minimum safety distance and complex gap within the range of altitude 3000 ~ 5500 m for 220 kV transmission line are calculated and analyzed by combining with the common altitude correction methods and the calculation of hazard scale. The results of this experimental investigation provide technical reference for engineering design and live working of 220 kV transmission line.