To improve the reliability of the protection system and reduce the maintenance cost of the power supply enterprise, it is necessary to evaluate the reliability of the state maintenance of the relay protection equipment in the substation. First, according to the failure mode and impact analysis method, the failure risk factors and influences of equipment are analyzed. Three aspects of equipment failure, namely, detectability, occurrence and severity, are selected. Taking the substation line protection device itself as an example, risk assessment is carried out and risk countermeasures are proposed to improve the reliability of relay protection equipment. Secondly, the state space method is introduced to establish the Markov model of substation relay protection equipment regular and state maintenance respectively. The rationality of the model is verified by a 220 kV line protection example data, and the conclusion is drawn that state maintenance can improve the availability of protection equipment. Finally, a comprehensive analysis of equipment reliability is carried out through simulation to verify the impact of periodic maintenance efficiency, the condition evaluation coefficient and the periodic maintenance cycle on the reliability of protective equipment. This work is supported by the Science and Technology Project of State Grid Corporation of China (No. 5212001900813).