Abstract: A fan control system having a temperature sensor, a temperature control module, a first logic, a second logic and a fan control circuit is provided to resolve the heat problem and the noise problem. The temperature sensor is used to detect the operation temperature of an integrated circuit, and the temperature control module receives the detected temperature to output a first logic signal. According to the first logic signal, the first logic outputs a second logic signal. One or more than one operation relationship between the fan rotation speed and operation temperature is set up in the second logic. According to the second logic signal, a curve showing the relationship between the fan rotation speed and the operation temperature is selected, and a second control signal is output. The control circuit can thus output a voltage to make the fan rotating, in responding to the second control signal.