This paper proposes an optimal maintenance interval decision scheme according to the reliability centered maintenance (RCM) concept for industrial plant based on the plant reliability evaluation. Monte-Carlo method is applied to simulate the multiple faults of electrical equipment in an industrial plant. In this paper path search method between the electrical loads and power source is proposed to judge whether the plant shutdown occurs due to electrical equipment fault. The Monte-Carlo method and the path search
method analyze the plant operating condition under a number of the electrical equipment fault conditions. The numerical examples by the electrical circuit model of an industrial plant demonstrate the proposed approach can give a practical solution for an optimal maintenance interval of an industrial plant.