A fan control circuit for controlling at least one fan of a power supply device includes a load sensing unit, a temperature sensing unit, a control unit connected to the load sensing unit, the temperature sensing unit and the fan, and a mode switching unit. The load sensing unit generates a load signal according to an output condition of the power supply device. The temperature sensing unit senses the temperature in the power supply device and generates a temperature signal. The control unit comprises a low-speed operating mode for controlling the fan according to the load signal, a mute mode for controlling the fan according to the temperature signal, and a full-speed operating mode for controlling the fan to run in a rated rotational speed. The mode switching unit controls the control unit to adjust the rotational speed of the fan by one of the three modes.