A method of protecting AT commands during the interaction between the AT command module of a mobile terminal and the serial communication unit of an external device, comprising the steps of: receiving AT command from the serial communication unit to the AT command module at an initial state; putting the AT command module into an ID verification mode, wherein the AT command module receives a username and password from the serial communication unit in turn, and verifies said received username and password; and putting the AT command module into an AT command processing state, when the ID verification is successful. Therefore, it's impossible for an illegal user to take the control of the mobile terminal through AT command.