A control system for a direct current, DC, fan, comprising a switching power supply and a control circuit, wherein, the switching power supply is connectable to a DC motor of the DC fan, and configured to convert an alternating current into a DC, and to output the DC to the DC motor; the control circuit is connected with the switching power supply and is further connectable to the DC motor respectively, and configured to output a working state signal to the switching power supply; the switching power supply is configured to output a corresponding working voltage to the DC motor according to the working state signal; the control circuit is configured to control a working state of the DC motor according to the working state signal, the switching power supply compnses a switching power supply reference voltage circuit, a switching power supply sampling circuit, a pulse width modulation circuit, a high frequency switching transformer circuit, a mams supply inputting-rectifying-filtering circuit and a high frequency rectifying-filtering output circuit, characterized in that, an input end of the switching power supply reference voltage circuit is connected with an output end of the control circuit, and the switching power supply sampling circuit is connected between an output end of the switching power supply reference voltage circuit and an input end of the pulse width modulation circuit; an output end of the pulse width modulation circuit and an output end of the mains supply inputting-rectifying-filtering circuit are connected with the high frequency switching transformer circuit, and an output end of the high frequency switching transformer circuit is connected with the high frequency rectifying-filtering output circuit; the switching power supply sampling circuit is connected with a voltage output end of the switching power supply reference voltage circuit and the high frequency rectifying-filtering output circuit, and the voltage output end of the switching power supply reference voltage circuit is connected with the high frequency rectifying-filtering output circuit; the switching power supply reference voltage circuit comprises a regulating resistor, a diode, second and third resistors (R2, R3), a capacitor and a voltage regulator source; one end of the regulating resistor is connected with the output end of the control circuit, another end of the regulating resistor is connected with a positive electrode of the diode, a negative electrode of the diode is connected respectively with one end of the second resistor, one end of the third resistor and a reference electrode of the voltage regulator source; another end of the second resistor is connected with the voltage output end of the switching power supply reference voltage circuit, and another end of the third resistor is connected with ground; one end of the capacitor is connected with the reference electrode of the voltage regulator source (ICl), another end of the capacitor is connected with the output end of the switching power supply reference voltage circuit, a cathode of the voltage regulator source is connected with the output end of the switching power supply reference voltage circuit, and an anode of the voltage regulator source is connected with the ground; the working voltage output by the switching power supply is changed by adjusting a resistance value of the regulating resistor, wherein, the smaller the working voltage is, the smaller a standby power consumption of the entire DC fan is.