A USB charger, a mobile terminal, and a charging method are provided. The USB charger for charging a mobile terminal, includes a first logic control unit through which bidirectional communication is established between the USB charger and the mobile terminal, wherein the first logic control unit is configured to: send, to the mobile terminal, a first signal which includes a maximum output capability of the USB charger; receive, from the mobile terminal, a second signal which indicates magnitude of a voltage requested by the mobile terminal; and adjust a voltage output from the USB charger to be consistent with the voltage requested by the mobile terminal. Accordingly, the USB charger and the mobile terminal can communicate with each other through a single signal wire. Thus, the voltage output from the USB charger can be intelligently controlled, so as to charge the mobile terminal in a fast, safe, and simply way.