The invention discloses a data migration method for a peer-to-peer (P2P) streaming media system. Media data is backed up in a P2P network by calculating a utility value of a data block and the transmission overhead ratio of neighbor nodes. By the method, the probability of invalidation of data distributed by a server in the network due to the dynamics of nodes can be reduced; and the bandwidth resources of the nodes are fully utilized, so that the load of the server is reduced, and the expandability of the system is improved.