Structural Health Monitoring (SHM) systems are used to monitor the operation and health status of large infrastructures. As wireless sensors require low power and are easily deployable, the Wireless Sensor Networks (WSN) are more commonly in the applications of applied to the system than the wired networks. However, SHM brings new challenges to WSNs such as engineering-driven optimal deployment, a large volume of data, sophisticated computing, etc., and so forth. In order to optimize the deployment of wireless sensors in the system, we introduce the reliability method to evaluate the network performance and consider an optimization problem: how to deploy the fewest backup sensor nodes such that the reliability is not no less than a given value R0 after the primary locations are have been determined. As a result, we prove that the reliability of G' (the added node is linked to every node in G) has been proved is higher than that of G. Accordingly, we propose an optimization optimized strategy of backup sensors. The simulation shows the effectiveness of the proposed strategy.