Embodiments of the present invention provide a data migration method and a communications node. The method includes: determining, by a first node in an OPUCn signal, a second tributary slot corresponding to a first tributary slot, where the second tributary slot is an idle tributary slot; and migrating, by the first node, a first low-order ODU service from the first tributary slot to the second tributary slot. In the embodiments of the present invention, by migrating, in an OPUCn signal, a first low-order ODU service of a first tributary slot to an idle second tributary slot, the existence of tributary slot fragments can be avoided, thereby improving utilization of network bandwidth resources.