The current implementation of BGP protocol has a variety of vulnerabilities and weakness. Monitoring BGP’s behavior is an effective way of improving the security of inter-domain routing. In this paper, a monitoring system for inter-domain routing security is presented. As for BGP routing table anomaly detection, an in-depth approach based on anomaly detection rules is designed; As for BGP UPDATE message anomaly detection, a real-time detection method is devised. By applying an improved spring-magnetic topological layout algorithm to the network topology display, our monitoring system provides a successful visualization for the detection results. The feasibility and validity of the monitoring approach are demonstrated by the detailed description of the final results analysis.