The invention provides a data migration method and device, a network attached storage device and a storage medium, and relates to the technical field of communication. The data migration method comprises: in the process that a source network attached storage device migrates data to a target network attached storage device, the target network attached storage device receives a data access request sent by a client; the target network attached storage device determining a to-be-accessed file root directory according to the to-be-accessed file path; determining that the to-be-accessed file is stored in a source network attached storage device according to the to-be-accessed file root directory, wherein the target network attached storage device stores a corresponding relationship between the root directory and the source network attached storage device; and the target network attached storage device forwarding the data access request to the source network attached storage device, receivesthe to-be-accessed file sent by the source network attached storage device, and sends the to-be-accessed file to the client. By means of the technical scheme, on-line data migration can be achieved under the condition that the data access service is not interrupted.