Since the lack of necessary security mechanisms, the Internet’s inter-domain routing system, mainly based on the Border Gateway Protocol (BGP), inevitably faces with serious security threats. Although there are many researches focus on the security of inter-domain routing and BGP, few people have quantified the routing security of the current BGP system effectively. Moreover, Internet operators do need useful information to judge security threats of their autonomous systems (ASes) and BGP routers. In this paper, we propose a security evaluation model, SEM, to assess security threats of the routing system. The basic idea of SEM is simple, namely, the security status of the whole system rests with its parts’. In addition, we quantify security threats status of the routing information from RouteViews using our model. The experimental results show that the model can provide intuitive security threat indices for BGP routers, various ASes and the BGP system respectively, and further more, it can provide valuable, intuitional curve for Internet operators.