IP geolocation determines geographical location by the IP address of Inteet hosts.IP geolocation is widely used by target advertising,online fraud detection,cyber-attacks attribution and so on.It has gained much more attentions in these years since more and more physical devices are connected to cyberspace.Most geolocation methods cannot resolve the geolocation accuracy for those devices with few landmarks around.In this paper,we propose a novel geolocation approach that is based on common routers as secondary landmarks (Common Routers-based Geolocation,CRG).We search plenty of common routers by topology discovery among web server landmarks.We use statistical leaing to study localized (delay,hop)-distance correlation and locate these common routers.We locate the accurate positions of common routers and convert them as secondary landmarks to help improve the feasibility of our geolocation system in areas that landmarks are sparsely distributed.We manage to improve the geolocation accuracy and decrease the maximum geolocation error compared to one of the state-of-the-art geolocation methods.At the end of this paper,we discuss the reason of the efficiency of our method and our future research.