terminal fetches the imsi of the user from the uim card and derives the nai of the user from the imsi and transmits the derived nai to the authentication server for authentication in the steps s 105 and s 106 according to the format imsi mycdma cn of the nai the mobile terminal adds mycdma cn subsequent to the fetched imsi and derives the nai in the format of imsi mycdma cn particularly the flow may proceed with step s 105 when the result of determination is u2018 no u2019 in the s 103 so that the nai authentication can succeed with the imsi even if the incorrect nai is written into the uim card furthermore with the step s 106 performed when the result of determination is u2018 no u2019 in the step s 102 it is possible for the uim card in which the identifier of supporting the md5 authentication method is stored to succeed in the nai authentication with the imsi stored in the uim card even if no nai is written into the uim card an embodiment of the invention further provides an nai authentication method for an evdo network in which only the steps s 101 s 102 and s 106 performed when the result of determination is u2018 no u2019 in s 102 so that the nai authentication can succeed with an imsi for a uim card in which an identifier of supporting an md5 authentication method is stored even if no nai is written into the uim card in order to succeed in nai authentication for a uim card in which an identifier of supporting an md5 authentication method is stored even if an nai in the uim card is incorrect an embodiment of the invention further provides an.