The invention discloses a method and system for data migration in a peer-to-peer (P2P) network. The method comprises the following steps that: when it is needed to carry out data migration, according to data version information of a node sending a join request, a withdrawal request or a load migration request as well as data version information of other active nodes in a current network, a configuration server distributes a data source node or a data target node to a node sending the request; the data source nodes compares current data version information of the migration data with data version information corresponding to the data target node, determines increment data and sends the increment data to the data target node; and the data target node restores data of the latest version according to the increment data and data stored by the data target node itself. According to the invention, the data volume of data migration in a P2P network can be substantially reduced, thereby ensuring normal working of the network.