A communications method, wherein the method comprises: obtaining, by a terminal device, a relay mode of the terminal device; and sending, by the terminal device, relay mode information of the terminal device and registration information to a relay device; wherein the registration information comprises identification information of the terminal device and/or identification information of a core network node with which the terminal device is registered; or the registration information is a registration request message; wherein the obtaining, by a terminal device, a relay mode of the terminal device comprises: obtaining, by the terminal device, the relay mode of the terminal device based on an idle-state camping manner of the terminal device; wherein the obtaining, by the terminal device, the relay mode of the terminal device based on an idle-state camping manner of the terminal device comprises: the relay mode of the terminal device is a long-term relay mode if the terminal device camps on an indirect transmission link that is a communication link between the terminal device and the relay device when the terminal device is in an idle state; or the relay mode of the terminal device is a temporary relay mode if the terminal device camps on a direct transmission link between the terminal device and an access network AN node when the terminal device is in an idle state. obtaining, by a terminal device, a relay mode of the terminal device; and sending, by the terminal device, relay mode information of the terminal device and registration information to a relay device; wherein the registration information comprises identification information of the terminal device and/or identification information of a core network node with which the terminal device is registered; or the registration information is a registration request message; wherein the obtaining, by a terminal device, a relay mode of the terminal device comprises: obtaining, by the terminal device, the relay mode of the terminal device based on an idle-state camping manner of the terminal device; wherein the obtaining, by the terminal device, the relay mode of the terminal device based on an idle-state camping manner of the terminal device comprises: the relay mode of the terminal device is a long-term relay mode if the terminal device camps on an indirect transmission link that is a communication link between the terminal device and the relay device when the terminal device is in an idle state; or the relay mode of the terminal device is a temporary relay mode if the terminal device camps on a direct transmission link between the terminal device and an access network AN node when the terminal device is in an idle state. obtaining, by the terminal device, the relay mode of the terminal device based on an idle-state camping manner of the terminal device; wherein the obtaining, by the terminal device, the relay mode of the terminal device based on an idle-state camping manner of the terminal device comprises: the relay mode of the terminal device is a long-term relay mode if the terminal device camps on an indirect transmission link that is a communication link between the terminal device and the relay device when the terminal device is in an idle state; or the relay mode of the terminal device is a temporary relay mode if the terminal device camps on a direct transmission link between the terminal device and an access network AN node when the terminal device is in an idle state. the relay mode of the terminal device is a long-term relay mode if the terminal device camps on an indirect transmission link that is a communication link between the terminal device and the relay device when the terminal device is in an idle state; or the relay mode of the terminal device is a temporary relay mode if the terminal device camps on a direct transmission link between the terminal device and an access network AN node when the terminal device is in an idle state.