Abstract: Based on a safety index evaluation system with hardware system, software system, human operation and environmental factors as the criterion layer was proposed, which the safety characteristics of a distributed fault diagnosis system was evaluated for some high voltage transmission line in south China. The calculation results showed that: after consistency check, the CR values of the established three-layer evaluation system are less than 0.1, which proves that the determined indicator system is reasonable; the operation and maintenance management and wind speed factor score are the lowest, which indicates that the system operation and maintenance after operation is not strict enough, and the emergency treatment of extreme environment is not sufficient; the final comprehensive evaluation value of the system is 86.73, indicating that the system is in a safe state.