Abstract: The present invention relates to IP network communication technology. It provides a kind of IP multicast data layer distribution method and system. The method includes: first code original multicast data into multiple sub-flow, separately specify different shunt sub-source for every sub-flow, distribute sub-group address, create sub-group state, etc, form shunt structure. Then the sink send join news to each shunt sub-source, join each shunt sub-source sub-group and become the leaf node of each sub-tree. And then each shunt sub-source determine the intermediate node according to the port receiving join news and construct multicast distribution-tree. If the overlapping portion between the multicast distribution trees produce congestion, in the congestion nodes network coding is used to eliminate congestion and construct coding sub-tree according to the way of building multicast distribution tree from the below of the coding nodes.