Concerning the network service failure caused by the virtual network function failure of the service function chain in the network function virtualization environment, a resource utility maximization backup method of virtual network function was put forward to improve the network reliability. First, the backup problem of virtual network functions was analyzed in detail and a reliability evaluation model was established; then a corresponding backup mechanism was put forward, and the advantages of the proposed mechanism over other mechanisms were proved. Secondly, a global backup method and a backup selection strategy were designed to select the corresponding virtual network functions until the reliability requirement was satisfied. Finally, simulation and experimental results showed that compared with GREP, JP+random selection and DSP+random selection, the proposed method achieved excellent performance in terms of reliability and resource utilization, especially improved the rate of request acceptance by 18.8%-25% and the resource utilization ratio by 15%-20%. The experimental results demonstrate that the proposed method can effectively utilize the resources to improve the network reliability.