Abstract: Live-working is an important method in ensuring the safe operation of distribution network. Although live-working has been widely applied in many low-altitude distribution lines, there is still some technology problems of live-working in high-altitude areas, such as the lack of safe insulation operating tools. With increasing altitude, the insulation tool flashover voltage will decrease, which is the key factor on researching minimum effective insulation length and developing high altitude work tools. In this paper, experimental study on minimum effective insulation length was implemented in high-altitude areas. Frequency discharge tests of operating and protective tools in different insulation lengths were performed in Yangbajing, Tibet (4300m), Lhasa, Tibet (3600m), Nyingchi, Tibet (2900m), Wuhan, Hubei (28m) respectively. The frequency discharge characteristic curves under different live-working tools were given. According to the above test results and the existing research in low altitude areas, the required minimum effective insulation length of live working tools within the range of altitude 3000m~4500m are calculated using the relative air pressure altitude correction method.