The "priority-based directed minimum spanning tree" (PST) is designed for Distributed Interactive Applications (DIAs) in which the data are delivered to the receiver node according to their priority; however PST can not balance the bandwidth usage among the nodes and the system will be unstable when its scale increases. This paper proposes a novel overlay multicast protocol named Priority Based Overlay Multicast (POM), which uses the priority, delay and available bandwidth to construct the multicast tree, besides a filtering mechanism is proposed to rebuild the tree when the available bandwidth shortage appears. The effectiveness of our protocol is demonstrated in the simulation results, showing that POM uses the available bandwidth efficiently, besides it keeps the system stable when its scale increases.