In order to reduce the blocking probability and improve energy efficiency in IP over flexible bandwidth optical networks, it is necessary to reduce the occupation of spectrum resources and the number of working network equipment when building the optical channels. Network equipment configuration with flexible line rates can improve the energy efficiency. Therefore, we propose an energy-efficient approach based on mixed-line-rate equipment configuration. To evaluate the performance of the proposed approach, we introduce a traditional energy-efficient approach with two line rates for comparison. The simulation results show that, compared with the traditional energy-efficient approach in IP over flexible bandwidth optical networks, our proposed energy-efficient approach can effectively reduce the blocking probability and network energy consumption by at least 20% with improved network performance.