The Cooperative Web Architecture (CWA) was proposed for relevant information retrieval using Web-Graph. In CWA, the Web servers maintain and deliver the neighboring link information (Web-Subgraph). When events that change the Web-Graph occur, the Web servers notify each other of the change in order to synchronize Web-Subgraphs. In this paper, we propose a synchronization method to solve a problem of inconsistency among Web-Subgraphs. This problem occurs because of the time difference between notifications. When multiple events occur simultaneously, the range of notification becomes invalid. Therefore the inconsistency problem occurs. We proposed two types of synchronization methods, then we compare and analyze their respective characteristics. Moreover we discuss feasibility from the viewpoint of traffic.