A USB interface power supply device for a time division multiple access load system, the time division multiple access load system is a radio frequency power amplifier load system which only works for a period of time Ton within one time cycle, wherein the device comprises: a USB interface, a soft-start circuit and a DC-DC direct current conversion circuit, wherein an output of the DC-DC direct current conversion circuit supplies power to the time division multiple access load system, and the power supply device further comprises a capacitor, the power supply device characterized in that it further comprises a detection circuit and a baseband control circuit, wherein: a first end of the capacitor is connected between an output of the soft-start circuit and an input of the DC-DC direct current conversion circuit, a second end of the capacitor is set to be grounded, and the capacitor is used for limiting an input current of the DC-DC direct current conversion circuit; the capacitor comprises a capacitance group and a switch group, one end of the capacitance group serves as the first end of the capacitor, the other end of the capacitance group serves as the second end of the capacitor, the switch group is connected with the baseband control circuit; a capacitance value of the capacitor is obtained through calculation with a following formula: C = U 0 × I 0 U i × η − I × Ton UC 1 − UC 2; wherein, UC1 is an initial voltage of the capacitor when the time division multiple access load system does not work, UC2 is a voltage of the capacitor when the time division multiple access load system works, U 0 is the voltage required by the time division multiple access load system, I 0 is the current required by the time division multiple access load system, U i is the input voltage of the DC-DC direct current conversion circuit, η is a conversion efficiency of the DC-DC direct current conversion circuit, and I is the maximum current allowed to be output by the USB interface; the detection circuit is configured to: be connected between the USB interface and an input of the soft-start circuit, and detect whether an output voltage of the USB interface supplied to the soft-start circuit is lower than a preset threshold value; and the baseband control circuit is configured to: connect with the detection circuit at one end, and connect with the switch group at the other end; when the detection circuit detects that the output voltage of the USB interface is lower than the preset threshold value, control a switch of the switch group being turned on, and the capacitance value of the capacitor being increased. a first end of the capacitor is connected between an output of the soft-start circuit and an input of the DC-DC direct current conversion circuit, a second end of the capacitor is set to be grounded, and the capacitor is used for limiting an input current of the DC-DC direct current conversion circuit; the capacitor comprises a capacitance group and a switch group, one end of the capacitance group serves as the first end of the capacitor, the other end of the capacitance group serves as the second end of the capacitor, the switch group is connected with the baseband control circuit; a capacitance value of the capacitor is obtained through calculation with a following formula: C = U 0 × I 0 U i × η − I × Ton UC 1 − UC 2; wherein, UC1 is an initial voltage of the capacitor when the time division multiple access load system does not work, UC2 is a voltage of the capacitor when the time division multiple access load system works, U 0 is the voltage required by the time division multiple access load system, I 0 is the current required by the time division multiple access load system, U i is the input voltage of the DC-DC direct current conversion circuit, η is a conversion efficiency of the DC-DC direct current conversion circuit, and I is the maximum current allowed to be output by the USB interface; the detection circuit is configured to: be connected between the USB interface and an input of the soft-start circuit, and detect whether an output voltage of the USB interface supplied to the soft-start circuit is lower than a preset threshold value; and the baseband control circuit is configured to: connect with the detection circuit at one end, and connect with the switch group at the other end; when the detection circuit detects that the output voltage of the USB interface is lower than the preset threshold value, control a switch of the switch group being turned on, and the capacitance value of the capacitor being increased.