The cooperative routing monitoring constructs a more complete global information view by information sharing among autonomous systems (ASes), which can eliminate the negative impact of the autonomous inter-domain routing system characteristic and improve the route monitoring ability of AS. This paper designs an information sharing mechanism called CoISM that is based on self-organization for the information sharing, which is the essential issue of cooperative route monitoring. CoISM leverages the localization caused by BGP policy to reduce and control the transmit range of information. It also uses information reflection to implement the information active push and builds AS profit on its altruistic information sharing behavior. This mechanism leads to information aggregation, as needed in self-organization, and facilitates cooperation among AS by its incentive. CoISM adopts a distributed architecture and has good expansibility and a lower communication overhead. In addition, it does not modify the BGP protocol, but supports an incremental deployment and can be used in many cross-domain cooperative management applications such as inter-domain routing monitoring, cooperative routing failure analysis, cooperative intrusion detection, and so on.