Embodiments of this application provide a session migration method and a device. The method includes: determining, by a source session management function entity, whether to update a session of a terminal device; and if the source session management function entity determines to update the session of the terminal device, retaining, by the source session management function entity, a context of a first session, and sending instruction information to a first device, where the instruction information is used to instruct the first device to trigger creation of a second session after the first device obtains to-be-sent data of the terminal device, the first session is a session created between the source session management function entity and the terminal device, the first device is the terminal device or a target mobility management function entity, and the second session is a session between a target session management function entity and the terminal device.