This paper defines the operational readiness of terminal high altitude antiballistic missile equipment under different maintenance systems, introduces how to calculate the operational readiness rates of equipment and establishing a repair delay time model. By utilizing the repair delay time to value the influence of maintenance systems on operational readiness rates is judged. Monte-Carlo method is used to simulate the model, and the demands of different maintenance systems on the repair delay time under the set operational readiness rates are got. The sensitivity analyses of MTBF and MTTR are made to validate that the parameter variety bound is reasonable. The results indicate that two-level maintenance is more beneficial to enhancing the operational readiness. The conclusion can be a reference for building terminal high altitude antiballistic missile equipment maintenance system.