Preventive maintenance of relay protection device can effectively improve the reliability of protection device. This paper uses Weibull distribution model and introduces failure rate increase factor to analyze protection device failure rate model under the action of preventive maintenance. On this basis, the preventive maintenance average cost function is taken as the objective function, and the reliability degree is taken as the constraints to construct the mode of protection device preventive maintenance which meet the requirements of reliability, and MATLAB software is used to solve the model to get the optimal maintenance cycle and maintenance times. Finally, the relationship between reliability and maintenance cost and the effect of failure rate on maintenance strategy are analyzed by examples. This paper has some reference significance for the maintenance department to make the maintenance plan.