Abstract: A distributed application consists of one or many members, such as CSCW or backup database application. In order to complete its tasks, one member usually not only sends multicast messages to other members, but also sends unicast messages to one or some members, and these messages form a causal dependence order relation. In order to support the communication between the group members and to support the development of the distributed applications, a new causal order unicast and multicast mixed communication protocol CR UMcast based on the vector time is proposed in this paper. This protocol allows the group members to send both multicast messages and unicast messages, and ensures the delivery of these messages in their causal precedence order.