A network locking method for a terminal, comprising: Utilizing an international mobile subscriber identity IMSI number carried on a subscriber identity module SIM card of the terminal to register the SIM card with a network, and obtaining a PLMN number of the network; and comparing the PLMN number of the network with a valid PLMN number segment pre-stored on the terminal and allowing or limiting, according to a comparison result, use of the SIM card by the terminal, wherein the valid PLMN number segment is implemented through codes, and the PLMN number segment is stored on a board inside the terminal; the method being characterized in that: the valid PLMN number segment is formed of first set digits of an IMSI number of one or multiple SIM cards allowed to be used by the terminal; and after an upgrade is performed on the board of the terminal, and said upgrade is completed, security verification is performed on the board, wherein the security verification comprises: calculating one Hash value according to multiple image files loaded on the board, and forming a digital certificate according to the Hash value; signing the digital certificate by using a private key of a preset pair of public and private keys, and putting the signed digital certificate into a boot image file of the board; and performing integrity verification on the digital certificate by using a public key of the preset pair of public and private keys, obtaining the Hash value in the digital certificate, and comparing the Hash value with a pre-stored valid Hash value, wherein if the two are not consistent, it is determined that the board is insecure; otherwise, it is determined that the board is secure. Utilizing an international mobile subscriber identity IMSI number carried on a subscriber identity module SIM card of the terminal to register the SIM card with a network, and obtaining a PLMN number of the network; and comparing the PLMN number of the network with a valid PLMN number segment pre-stored on the terminal and allowing or limiting, according to a comparison result, use of the SIM card by the terminal, wherein the valid PLMN number segment is implemented through codes, and the PLMN number segment is stored on a board inside the terminal; the method being characterized in that: the valid PLMN number segment is formed of first set digits of an IMSI number of one or multiple SIM cards allowed to be used by the terminal; and after an upgrade is performed on the board of the terminal, and said upgrade is completed, security verification is performed on the board, wherein the security verification comprises: calculating one Hash value according to multiple image files loaded on the board, and forming a digital certificate according to the Hash value; signing the digital certificate by using a private key of a preset pair of public and private keys, and putting the signed digital certificate into a boot image file of the board; and performing integrity verification on the digital certificate by using a public key of the preset pair of public and private keys, obtaining the Hash value in the digital certificate, and comparing the Hash value with a pre-stored valid Hash value, wherein if the two are not consistent, it is determined that the board is insecure; otherwise, it is determined that the board is secure. the valid PLMN number segment is formed of first set digits of an IMSI number of one or multiple SIM cards allowed to be used by the terminal; and after an upgrade is performed on the board of the terminal, and said upgrade is completed, security verification is performed on the board, wherein the security verification comprises: calculating one Hash value according to multiple image files loaded on the board, and forming a digital certificate according to the Hash value; signing the digital certificate by using a private key of a preset pair of public and private keys, and putting the signed digital certificate into a boot image file of the board; and performing integrity verification on the digital certificate by using a public key of the preset pair of public and private keys, obtaining the Hash value in the digital certificate, and comparing the Hash value with a pre-stored valid Hash value, wherein if the two are not consistent, it is determined that the board is insecure; otherwise, it is determined that the board is secure. calculating one Hash value according to multiple image files loaded on the board, and forming a digital certificate according to the Hash value; signing the digital certificate by using a private key of a preset pair of public and private keys, and putting the signed digital certificate into a boot image file of the board; and performing integrity verification on the digital certificate by using a public key of the preset pair of public and private keys, obtaining the Hash value in the digital certificate, and comparing the Hash value with a pre-stored valid Hash value, wherein if the two are not consistent, it is determined that the board is insecure; otherwise, it is determined that the board is secure.