An information writing method, comprising: acquiring (101, 201), by a terminal, code number information of a Subscriber Identification Module, SIM, card, the code number information being verification information during access of the SIM card to a network of an operator; sending, by the terminal, the code number information to a Card Operating System, COS, of the SIM card through an original interface in an operating system, the original interface being a communication interface programmed for transmission of other information between the operating system and the COS; the other information is information transmitted through the original interface when an original function of the original interface is implemented; and writing, by the COS, the code number information into the SIM card; wherein sending, by the terminal, the code number information to the COS of the SIM card through the original interface in the operating system comprises: encrypting the code number information and obtaining said other information packaged from the encrypted code number information; and sending said other information packaged from the encrypted code number information to the COS through the original interface in the operating system; wherein writing, by the COS, the code number information into the SIM card comprises: decrypting, by the COS, the received other information; in case of successful decryption, detecting, by the COS, whether the decrypted information meets a code number information format; and when the decrypted information meets the code number information format, determining, by the COS, that the decrypted information is the code number information, and writing the code number information into the SIM card. acquiring (101, 201), by a terminal, code number information of a Subscriber Identification Module, SIM, card, the code number information being verification information during access of the SIM card to a network of an operator; sending, by the terminal, the code number information to a Card Operating System, COS, of the SIM card through an original interface in an operating system, the original interface being a communication interface programmed for transmission of other information between the operating system and the COS; the other information is information transmitted through the original interface when an original function of the original interface is implemented; and writing, by the COS, the code number information into the SIM card; wherein sending, by the terminal, the code number information to the COS of the SIM card through the original interface in the operating system comprises: encrypting the code number information and obtaining said other information packaged from the encrypted code number information; and sending said other information packaged from the encrypted code number information to the COS through the original interface in the operating system; encrypting the code number information and obtaining said other information packaged from the encrypted code number information; and sending said other information packaged from the encrypted code number information to the COS through the original interface in the operating system; wherein writing, by the COS, the code number information into the SIM card comprises: decrypting, by the COS, the received other information; in case of successful decryption, detecting, by the COS, whether the decrypted information meets a code number information format; and when the decrypted information meets the code number information format, determining, by the COS, that the decrypted information is the code number information, and writing the code number information into the SIM card. decrypting, by the COS, the received other information; in case of successful decryption, detecting, by the COS, whether the decrypted information meets a code number information format; and when the decrypted information meets the code number information format, determining, by the COS, that the decrypted information is the code number information, and writing the code number information into the SIM card.