A mobile network access device, comprising: a Secure Digital, SD, slave controller, configured to send data or a command to a storing unit or a baseband processing unit according to a logical address in an SD command; wherein the SD slave controller is configured to send the data or command to the storing unit if the logical address in the SD command corresponds to any physical address and wherein the SD slave controller is configured to send the data or command to the baseband processing unit if the logical address in the SD command corresponds to no physical address, the baseband processing unit, configured to send the data or command to an application module corresponding to the baseband processing unit if the SD slave controller determines to send the data or command to the baseband processing unit according to the logical address in the SD command; and the storing unit, configured to use a physical address corresponding to the logical address to read and write the storing unit according to the SD command if the SD slave controller determines to send the data or command to the storing unit according to the logical address in the SD command; the device further comprises an SD port, a Radio Frequency, RF, processing unit, a power supply managing unit, a Subscriber Identity Module, SIM, unit, and an antenna; the SD port, configured to provide a connection between the SD slave controller of the mobile network access device and an SD master controller of a terminal device; the RF processing unit is connected to the baseband processing unit and the antenna, and is configured to receive and transmit high-frequency signals through the antenna in wireless mode, and get connected to a network; the power supply managing unit is configured to manage power supply of the device, and supply power to the RF processing unit, SIM unit, storing unit, and baseband processing unit; and the SIM unit is configured to store user information. a Secure Digital, SD, slave controller, configured to send data or a command to a storing unit or a baseband processing unit according to a logical address in an SD command; wherein the SD slave controller is configured to send the data or command to the storing unit if the logical address in the SD command corresponds to any physical address and wherein the SD slave controller is configured to send the data or command to the baseband processing unit if the logical address in the SD command corresponds to no physical address, the baseband processing unit, configured to send the data or command to an application module corresponding to the baseband processing unit if the SD slave controller determines to send the data or command to the baseband processing unit according to the logical address in the SD command; and the storing unit, configured to use a physical address corresponding to the logical address to read and write the storing unit according to the SD command if the SD slave controller determines to send the data or command to the storing unit according to the logical address in the SD command; the device further comprises an SD port, a Radio Frequency, RF, processing unit, a power supply managing unit, a Subscriber Identity Module, SIM, unit, and an antenna; the SD port, configured to provide a connection between the SD slave controller of the mobile network access device and an SD master controller of a terminal device; the RF processing unit is connected to the baseband processing unit and the antenna, and is configured to receive and transmit high-frequency signals through the antenna in wireless mode, and get connected to a network; the power supply managing unit is configured to manage power supply of the device, and supply power to the RF processing unit, SIM unit, storing unit, and baseband processing unit; and the SIM unit is configured to store user information.