The successful authenticating of a Network Access Identifier (NAI) process is enabled by an authenticating method and a mobile terminal for a Code Division Multiple Access (CDMA) EVolution to packet Data Optimized (EVDO) network. The authenticating method for the EVDO network includes an NAI authenticating and a Challenge Handshake Authentication Protocol (CHAP) authenticating, in which the NAI authenticating method includes: when it is determined that the identifier supporting a Message-Digest 5 (MD5) authenticating method is stored in a User Identity Model (UIM) (S101), the NAI of a user is read from the UIM (S102); a judgment is made whether the NAI is correct when the NAI of the user is read from the UIM (S103); if the result of the judgment is yes, the read NAI is transmitted to an authentication server to perform an authentication (S104); if the result of the judgment is no, the International Mobile Subscriber Identity (IMSI) of the user is read from the UIM; and the NAI of the user is obtained according to the IMSI and the obtained NAI is transmitted to the authentication server to perform the authentication (S105).