Based on the reliability theory, the probability perturbation technique, the reliability sensitivity technique and robust design were employed to discuss the reliability-based robust optimization problem of structure system with multiple failure modes. By means of the probability network evaluation technique (PNET), the representative failure modes of structure system were defined. Then, the reliability and the reliability sensitivity of the system were obtained. By integrating the reliability sensitivity into the reliability-based optimization design model, the robust reliability design of structure system was discussed. According to the numerical results, the method proposed is validated to be practical and effective.