Advanced computer network can realize the bulk data transfer and real time control with high reliability and precision. Its availability not only depends on the connectivity of topological structure but also resies on its operational performance. Based on new network description, this paper provides the availability model of link and nodes that can be calculated with Generalized Stochastic Petri Net (GSPN). The main contribution of this paper focuses on the routing selection and performance evaluation. Working on the network performance by queueing theory, it concludes that the throughput and time delay are two impurtant performance indices in network. With Power formula, this paper presents the integrated availability model considering both topologic reliability and operational performance, which can realize the availability analysis perfectly from the point of view of a user.