Embodiments of the prevent invention provide a network access authentication method and device. The method comprises: receiving an authentication request message sent by a first serving network, wherein the authentication request message carries a user equipment pseudonym identifier generated by a user equipment; determining whether a local user equipment pseudonym identifier is asynchronous with the user equipment pseudonym identifier generated by the user equipment; and obtaining, if the determination result is yes, an encrypted international mobile subscriber identity (IMSI) to carry out network access authentication on the user equipment. The embodiments of the present invention can solve the problem that a network access process in the related art does not provide a processing method for the case where the user equipment pseudonym identifier in the user equipment is asynchronous with the user equipment pseudonym identifier in a home network.