Abstract: A new definition for the size of community was proposed based on the CNM algorithm, which was to solve the problem of excessive size of community exist in the past algorithm for detecting community. The new partition algorithm was called CLCNM. The results of community partition showed that the improved algorithm was superior to the CNM algorithm on the number of community and modules. On this basis, the relation between community partition and geography was studied, and a conception of the similarity of address prefix was proposed, which indicated that the greater similarity, the more obvious effect of relation between community and geography. The results of community partition by CLCNM showed that the communities of IPv6 topology had an obvious effect of geography, that was the sub-group node located in adjacent geographical location. This conclusion can provide advice to the re-deployment of network topology.