Abstract—For the purposes of monitoring or controlling, numerous of wireless sensors might be widely deployed to obtain and send information in the wireless sensor network (WSN). The applications of the WSN can be found in environment monitoring, industrial process monitoring and controlling, health caring, smart homes building and traffic controlling. To sending message efficiently in WSN, routing problem is an essential issue and must be taken into consideration. Instead of considering the problem routing among immovable sensors (nodes) in WSN, this paper discusses the problem of routing among moveable nodes. Although many routing protocols have been proposed for message delivering, some of them work well for sending message to single destination but not for multiple destinations. Due to the necessity in some applications, multicast service has been an indispensable function in the mobile WSN. Since Weight-based Clustering Multicast Routing Protocol (WCMRP) is one of the proposed protocols for multicast outperforming in the mobile network, with little modification on weight function, an improved WCMRP protocol (IWCMRP) is proposed for a mobile wireless sensor network. To illustrate the performance of IWCMRP, the results of simulation running with NS-2 are given, which shows IWCMRP performs better than WCMRP.