Abstract: Transformer operation and maintenance methods affect its operational reliability and maintenance costs, thus affecting the life cycle cost. The Weibull distribution failure probability model is employed in this paper. The life efficiency index is proposed and the life efficiency index (LEI) model is established to quantitatively measure the effect of maintenance on increasing the operating life of the transformer. The total life cycle cost of transformers from design, purchase, maintenance to decommissioning was analyzed. Taking the lowest average annual cost per life cycle as the objective function, under the constraints of operational reliability, maintenance levels, and life efficiency indicators, the cuckoo algorithm is used to optimize the maintenance year, maintenance level, and operating life parameters in the operation and maintenance strategy. Comparing the optimization results with Particle Swarm Optimization (PSO) and Genetic Algorithm (GA), the results show that the results obtained by the cuckoo algorithm are better, and the annual average cost and life efficiency indicators can be further reduced, which can provide certain guarantees for transformer operation and maintenance. 1. LEI model Lifetime efficiency index: LEI is described as the lifetime without maintenance is divided to the lifetime with maintenance. The LEI model is defined in this paper. It shows that how much the lifetime of equipment changes with and without maintenance. Transformer failure probability distribution model, influence of maintenance on failure probability, definition of life efficiency index and mathematical expression are introduced. 1.1 Transformer failure probability model This paper assumes that the transformer failure model is Weibull distribution. 1.2 The influence of maintenance on failure probability The effect of maintenance on the probability of failure are analyzed, quantitatively indicating the extent to which different levels of maintenance reduce the probability of failure. 1.3 LEI model The definition of the life efficiency index is given. Based on the Weibull distribution of the failure probability distribution, the mathematical equation of the life efficiency index and the method of solving the life efficiency index is derived. 2. Life cycle cost of transformer Transformer life cycle cost model and objective function and constraints are introduced. 2.1 Transformer life cycle cost model The transformer life cycle cost model includes operating costs, maintenance costs, outage costs, and generalized depreciation costs. Mathematical models and calculation equations for various costs. 2.2 Objective function and constraints The lowest average annual cost is the objective function, and the influencing factors include the number of overhauls, the years of maintenance, the level of maintenance, and the operating period. The constraints include the reliability, life efficiency, and maintenance level constraints. 3. Transformer annual average cost optimization based on cuckoo algorithm The principle of the cuckoo algorithm and the main steps of the cuckoo algorithm to optimize the life cycle cost is introduced. 3.1 The principle of the cuckoo algorithm 3.2 The main steps of the cuckoo algorithm to optimize the life cycle cost 4. Case Analysis Taking a transformer data as an example, the genetic algorithm, particle swarm algorithm, and cuckoo algorithm are respectively used to solve the objective function. 6. Conclusion The average annual cost of the cuckoo algorithm is the lowest, the iteration convergence rate is the fastest, and better search results can be obtained.