A method for handover to a relay node, a related device, and a system, where the method includes sending, by a base station of a target cell in an initial random access procedure initiated by a terminal device for the target cell, indication information to the terminal device using a random access message to instruct the terminal device to report information about a candidate relay device corresponding to the terminal device, receiving the information about the candidate relay device from the terminal device determining, in the candidate relay device according to the information about the candidate relay device, a target relay node used for relay communication between the terminal device and the base station, and handing over the terminal device to the target relay node.