According to the analysis of lightning trip data of three 500 kV transmission lines between Ertan hydropower station and Puti switch station in 4 years from 2007 to 2010, aiming at various aspects of characteristics of trip frequency, trip section and corresponding terrain feature of transmission lines between Ertan and Puti, this paper presents some suggestions on improving the level of lightning protection in specific sections with big density of ground flash. This paper provides some references for power departments to improve the lightning protection of transmission lines.