Network virtualization as an important research, will have a far-reaching effect on next generation network. However, the current studies of virtual network (VN) pay more attention to the utilization of the substrate network (SN) and optimization of mapping algorithms, whereas the course of mapping they ignore some serious weaknesses such as substrate network's high availability. This paper we forces on two aspects to improve high availability of VN. First, pre-optimizing the network topology based on the index of node & link failure rate. Second, we propose a high availability mapping algorithm (HAMA), which is avoid of frequently mapping taken place in when it is a heavy burden for nodes and links. Simulation and analysis demonstrate that the proposed method can effectively ensure high availability of virtual networks.