Based on the actual state of power equipment, this paper establishes an optimal service life evaluation model for in-service equipment based on state linkage, in order to make a scientific optimal service life prediction for equipment in service, maintain power supply reliability and improve economic efficiency for power supply enterprises. Considering individual differences and taking health index and environment factor into account, a state linked failure rate prediction model is established to improve the prediction of reliability factors. Using the fuzzy age reduction model, taking the reliability and the economy into account, an optimal service life evaluation model for in-service equipment is proposed, taking the minimum annual life cycle cost as a goal. Taking the transformer as an example, this paper makes a comparative analysis on the optimal service life from two dimensions, in-service time and current health index. The numerical results show that the proposed optimal service life evaluation model can reasonably set the optimum service life, which can provide theoretical reference for the maintenance work and retirement arrangement of power equipment.