The invention discloses an online data migration method, which is used for solving the technical problems of low efficiency and low universality of the conventional data migration method. The technical scheme comprises the following steps of: copying data in a logic unit number (LUN) of a source logic unit into the LUN of a target logic unit, and continuously running a system and a service in a data migration process; simultaneously copying the data updated into the LUN of the source logic unit into the LUN of the target logic unit in the migration process; simultaneously reflecting updating and copying processes by using a single bitmap mapping table; and after the data migration process is finished, using and updating used equipment at any time, and deleting the used equipment. The system and the service are continuously run in the data migration process, so the data migration efficiency and the data migration universality are improved.