Monitoring network resource can provide effective support for better virtual network service under the environment of network virtualization.The management structure of virtual network resource is built up， then a method based on monitoring agent is used for realizing real-time monitoring of network resource.Considering synthetically the bandwidth， delay of reporting monitoring information and load of network node， a binary combinatorial optimal model for the deployment of monitoring agent is established， which is solved to find the approximate optimal solution by improved particle swarm algorithm.The simulation result indicates that the deployment of monitoring agent generated by proposed method has fine performance.