A security parameter transmission method, comprising: receiving, by a network side device, radio resource connection management signaling sent by a first terminal device, wherein the first terminal device has a relay function, and the radio resource connection management signaling is sent by a second terminal device to the first terminal device; determining, by the network side device, an identifier of the second terminal device that generates the radio resource connection management signaling, and obtaining a security parameter corresponding to the identifier of the second terminal device; and sending, by the network side device, the obtained security parameter to the second terminal device by using the first terminal device; wherein the sending, by the network side device, the obtained security parameter to the second terminal device by using the first terminal device comprises: generating, by the network side device, a secure transmission mode request, wherein the secure transmission mode request carries the security parameter; and sending, by the network side device, the secure transmission mode request to the first terminal device, so that the first terminal device forwards the secure transmission mode request to the second terminal device; the method being characterized in that the secure transmission mode request further carries the identifier of the second terminal device, so that the first terminal device forwards the secure transmission mode request to the second terminal device based on the identifier of the second terminal device carried in the secure transmission mode request. receiving, by a network side device, radio resource connection management signaling sent by a first terminal device, wherein the first terminal device has a relay function, and the radio resource connection management signaling is sent by a second terminal device to the first terminal device; determining, by the network side device, an identifier of the second terminal device that generates the radio resource connection management signaling, and obtaining a security parameter corresponding to the identifier of the second terminal device; and sending, by the network side device, the obtained security parameter to the second terminal device by using the first terminal device; wherein the sending, by the network side device, the obtained security parameter to the second terminal device by using the first terminal device comprises: generating, by the network side device, a secure transmission mode request, wherein the secure transmission mode request carries the security parameter; and sending, by the network side device, the secure transmission mode request to the first terminal device, so that the first terminal device forwards the secure transmission mode request to the second terminal device; generating, by the network side device, a secure transmission mode request, wherein the secure transmission mode request carries the security parameter; and sending, by the network side device, the secure transmission mode request to the first terminal device, so that the first terminal device forwards the secure transmission mode request to the second terminal device; the method being characterized in that the secure transmission mode request further carries the identifier of the second terminal device, so that the first terminal device forwards the secure transmission mode request to the second terminal device based on the identifier of the second terminal device carried in the secure transmission mode request.