In many countries including Korea, many researchers have focused on the optimum maintenance method and system of deteriorating structures. A practical and realistic method is proposed to establish the lifetime optimum maintenance strategies for deteriorating steel bridges considering the life-cycle performance and cost. And a system is developed based on the method in order to overcome the limit of the exiting bridge maintenance systems. The proposed method and development system can produce the set of optimum tradeoff maintenance scenarios among other conflicting objectives such as minimizing cost and maximizing performance. Therefore the system can be utilized as a prototype for a next-generation bridge maintenance system to actualize the preventive maintenance of bridges. A multi-objective combinatorial optimization problem is formulated and a genetic algorithm is applied to generate the tradeoff maintenance scenarios which satisfy the balance among the conflicting objectives such as the performance and cost during the bridge lifetime. By using the developed program, this study proposes a process of optimum maintenance scenario applying to the steel girder bridge of the Korean National Road.