The invention relates to a multicast communication method, a relay node and a wireless network system using the method. The multicast communication method is suitable for transferring a multicast packet from a first member node to a plurality of second member nodes in the wireless network system, wherein the second member node and the first member node belong to the same group and can be communicated with each other through a plurality of non-member nodes. The multicast communication method comprises the following steps of: recording the number and the distance of the second member node, receiving the multicast packet from the first member node, determining a waiting time according to the number and the distance of the second member node, monitoring whether other nodes broadcast the multicast packet or not during the waiting time, and stopping to broadcast the multicast packet when other nodes broadcast the multicast packet to all second member nodes, otherwise, broadcasting the multicast packet after the waiting time becomes due.