A backup resource reoptimization scheme is presented. The presented scheme dynamically adjusts backup lightpaths and reoptimizes the optical network resources. Link load and link reliability that vary with time are considered in this reoptimization scheme. Reserved backup lightpaths are dynamically adjusted to avoid traversing both the heavily loaded links and the unreliable links during the network operation. A heuristic algorithm is presented to achieve fast online backup resource reoptimization. Simulation results show that the presented backup resource reoptimization scheme reduces the network blocking probability while improving the robustness of optical networks against multiple link failures, and thus improves the network performance.