Military information systems are playing an increasingly important role in system operations at the information age, and comprehensive evaluation of performance is helpful to grasp the overall situation of system operation and maintenance. In view of the system operation and maintenance performance evaluation problem in consideration of time stability, first, a 6+20 twoC-level index system is built up. Secondly, a performance evaluation model in consideration of time stability is established. Based on comprehensive subjective and objective information, the optimal index weights are determined by adopting the Lagrange multiplier method, After that, the weight of the evaluation time is determined with the variance value as the optimization goal. And the system operation and maintenance performance evaluation results are generated on the basis of determining index and evaluation time weights. Finally, the proposed method is verified by simulation examples.