Abstract: Based on the gas emission characteristics of natural gas purification plant and concentration distribution prediction in atmosphere during the development process of high sour gas filed, insulation performance analysis of acid gases on the 220 kV line was conducted, taking Puguang gas field as example. Insulating property of polluted insulator and the air under simulated acid mist environment were measured respectively. The results showed that flashover voltage of insulator dropped about 20% under the action of salt mist. Insulating strength of the air dropped about 15.1% when the pH value of mist was 3. After the combination of acid mist (pH=3) and class Ⅱ air pollution, insulating strength of the air dropped about 23.2%. Lightning withstand level of electric transmission line decreased 20% approximately under acid rain and acid mist environment with pH value of 3. Combined the laboratory analysis results and practical situation in Puguang gas field, the protective measures of electric transmission line in acid gas field were analyzed.