Embodiments of the present invention disclose a relay node authentication method, apparatus, and system. The method provided in an embodiment of the present invention includes: sending, by a relay node, an authentication request message to a peer node, where the authentication request message includes a certificate of the relay node, so that the peer node authenticates the relay node according to the certificate of the relay node, where the peer node is a network side node or a security gateway in a security domain where the network side node is located; and receiving, by the relay node, an authentication response message sent by the peer node, where the authentication response message includes a certificate of the peer node, and authenticating the peer node according to the certificate of the peer node.