A method for downloading software to a mobile terminal, comprising: A) when software is required to be downloaded from a computer terminal to the mobile terminal, a software downloading tool on the computer terminal is controlled to establish a connection with the mobile terminal by means of a preloader port of the mobile terminal and to send a download agent, DA, to the mobile terminal; and B) a preloader program of the mobile terminal checks whether the download agent is signed and encrypted by a private key which is matched with a Rivest-Shamir-Adleman, RSA, public key preset in the preloader program, and if yes, the mobile terminal starts the download agent to download the software, wherein the preloader program is a bootloader in initial work procedures of the mobile terminal and the preloader port is a port used to communicate with the preloader program, wherein the Step A) comprises: A1) when the mobile terminal is connected to the computer terminal via a Universal Serial Bus, USB, interface and when the software is required to be downloaded from the computer terminal to the mobile terminal, the mobile terminal itself detects whether any software exists in the mobile terminal; A2) when any software exists in the mobile terminal, the software downloading tool on the computer terminal is controlled to establish the connection with the mobile terminal by means of the preloader port of the mobile terminal and to perform the verification on the download agent in downloading the software required to be downloaded; A3) the software downloading tool on the computer terminal sends the download agent to the mobile terminal; and A4) when no software exists in the mobile terminal, the software downloading tool on the computer terminal is controlled to establish a connection with the mobile terminal by means of a Boot ROM, BROM, port of the mobile terminal and not to perform the verification on the download agent in downloading the software required to be downloaded, wherein BROM is a load program for a central processing unit, CPU, chip, in which data is unerasable, a BROM port is a port used to communicate with the BROM. A) when software is required to be downloaded from a computer terminal to the mobile terminal, a software downloading tool on the computer terminal is controlled to establish a connection with the mobile terminal by means of a preloader port of the mobile terminal and to send a download agent, DA, to the mobile terminal; and B) a preloader program of the mobile terminal checks whether the download agent is signed and encrypted by a private key which is matched with a Rivest-Shamir-Adleman, RSA, public key preset in the preloader program, and if yes, the mobile terminal starts the download agent to download the software, wherein the preloader program is a bootloader in initial work procedures of the mobile terminal and the preloader port is a port used to communicate with the preloader program, A1) when the mobile terminal is connected to the computer terminal via a Universal Serial Bus, USB, interface and when the software is required to be downloaded from the computer terminal to the mobile terminal, the mobile terminal itself detects whether any software exists in the mobile terminal; A2) when any software exists in the mobile terminal, the software downloading tool on the computer terminal is controlled to establish the connection with the mobile terminal by means of the preloader port of the mobile terminal and to perform the verification on the download agent in downloading the software required to be downloaded; A3) the software downloading tool on the computer terminal sends the download agent to the mobile terminal; and A4) when no software exists in the mobile terminal, the software downloading tool on the computer terminal is controlled to establish a connection with the mobile terminal by means of a Boot ROM, BROM, port of the mobile terminal and not to perform the verification on the download agent in downloading the software required to be downloaded, wherein BROM is a load program for a central processing unit, CPU, chip, in which data is unerasable, a BROM port is a port used to communicate with the BROM.