This application discloses a network authentication method, and a related device and system. The method includes: receiving, by a network authentication network element, an access request sent by user equipment, where the access request includes identification information of the user equipment; verifying, by the network authentication network element, whether the identification information is valid, and if the identification information is valid, determining, based on the identification information, a slice authentication network element corresponding to the user equipment; and sending, by the network authentication network element, the identification information to the slice authentication network element corresponding to the user equipment, where the identification information is used by the slice authentication network element corresponding to the user equipment to generate authentication data for the user equipment and initiate a user authentication request to the user equipment by using the authentication data.