Abstract: A fan control circuit is installed on a fan and connected with a control source which outputs a fan starting signal to the fan control circuit based on a load state. The fan control circuit includes a switch and a control module, the switch is installed on the fan and is directly operated to switch to one of a plurality of states, and the control module is connected with the switch and a motor coil installed on the fan. The control module outputs a driving signal to the motor coil based on the fan starting signal. The driving signal and a rotating speed of the fan define a rotating speed curve. A change of the states of the switch changes a slope of the rotating speed curve of the fan.