Embodiments of the present disclosure disclose a network authentication method, a relay node, and a related system. The system includes user equipment, a relay node, and a cellular network authentication network element. The user equipment is configured to send a first authentication message to the relay node; the relay node is configured to receive first authentication messages, and generate first encrypted information by using an aggregation algorithm based on first encrypted identifiers in the first authentication; the cellular network authentication network element is configured to receive a first aggregation message, and when verifying, by using the first encrypted information, that information in the first aggregation message is correct, send a first response message to the relay node; and the user equipment is configured to generate a session key between the user equipment and the cellular network authentication network element when verifying that information in the first response message is correct.