Since the evaluation factors possess grey fuzzy and interval values’ features while the maintenance decision-making of relay protection is performed, an interval numbers grey fuzzy theory based maintenance decision-making method is proposed. On the basis of deciding six principal factors of influencing maintenance decision-making of relay protection, an evaluation system including four maintenance projects is established. Considering the interaction between the grey part and fuzzy part of evaluation factors, this ordered weighted averaging (OWA) operator is used to aggregate the factor values of every project, and the interval grey fuzzy numbers are calculated, the comprehensive evaluation value of every project is worked out, then a more practical maintenance project is preferred. Taking a type RCS-931BM relay protection device and the secondary circuit for example, the optimal maintenance project is selected and the feasibility and validity of the proposed method is validated.