A charging system, comprising a charger and a smart terminal, wherein the charger comprises: - a first universal serial bus, USB, interface; - an AC/DC module, configured to convert AC voltage to DC voltage, and comprising at least two output ends, each configured to output a corresponding one of at least two different charging voltages; - a gating module in form of a single-pole multi-throw analog switch, configured to selectively connect one of the output ends of the AC/DC module to a power supply bus, VBUS, end of the first USB interface; and - a first control module, configured to control, according to level states of a positive data line, D+, end and a negative data line, D-, end of the first USB interface, the gating module to select one of the output ends of the AC/DC module while a charging current output by the charger is constant; - the AC/DC module being connected to the first control module and being connected to the VBUS end of the first USB interface through the gating module; - the first control module being connected to the gating module, and the D+ end, the D- end, and an identification, ID, end of the first USB interface; and the smart terminal comprises: - a battery; - a second USB interface electrically connectable to the first USB interface; - a charge management module, configured to charge the battery and control a charging voltage curve to be constant; and - a second control module, configured to monitor a capacity of the battery and a charging current output by the charge management module and control level states of a D+ end and a D- end of the second USB interface according to the capacity of the battery and a charging current output by the charge management module; wherein - the charge management module is connected to a VBUS end of the second USB interface, the second control module, and a positive terminal of the battery, - a negative terminal of the battery is grounded; and - the second control module is connected to the charge management module, and the D+ end, the D- end, and an ID end of the second USB interface. - a first universal serial bus, USB, interface; - an AC/DC module, configured to convert AC voltage to DC voltage, and comprising at least two output ends, each configured to output a corresponding one of at least two different charging voltages; - a gating module in form of a single-pole multi-throw analog switch, configured to selectively connect one of the output ends of the AC/DC module to a power supply bus, VBUS, end of the first USB interface; and - a first control module, configured to control, according to level states of a positive data line, D+, end and a negative data line, D-, end of the first USB interface, the gating module to select one of the output ends of the AC/DC module while a charging current output by the charger is constant; - the AC/DC module being connected to the first control module and being connected to the VBUS end of the first USB interface through the gating module; - the first control module being connected to the gating module, and the D+ end, the D- end, and an identification, ID, end of the first USB interface; and - a battery; - a second USB interface electrically connectable to the first USB interface; - a charge management module, configured to charge the battery and control a charging voltage curve to be constant; and - a second control module, configured to monitor a capacity of the battery and a charging current output by the charge management module and control level states of a D+ end and a D- end of the second USB interface according to the capacity of the battery and a charging current output by the charge management module; wherein - the charge management module is connected to a VBUS end of the second USB interface, the second control module, and a positive terminal of the battery, - a negative terminal of the battery is grounded; and - the second control module is connected to the charge management module, and the D+ end, the D- end, and an ID end of the second USB interface.