In recent years, the application of transmission channel environment on-line monitoring device has played an important role in improving the level of power grid support capability. In order to further optimize the deployment of monitoring devices, it is necessary to establish a sitting method which adequately considers the environmental characteristics. Based on the analysis of the altitude data at transmission line tower location, a sitting method of monitoring device considering terrain characteristics is established. According to altitude data, five terrain categories, including "Uphill", "Downhill", "Top", "Valley" and "Flat", are proposed, and the terrain judgment method of line tower is formed. On this foundation, a sitting method of monitoring device is set up, and the influence of mountainous terrain is considered, typical monitoring blind areas correction is completed. The analysis of calculation results show that this method can focus on mountain coverage on the basis of whole section monitoring at transmission channel, and the density of monitoring device can well match with the terrain. An application of the research can provide guidance for the development of transmission channel monitoring.