A fan detection method, a fan detection chip and a fan detection system using the same are disclosed. The fan detection method is applied to a fan detection chip including a first pin, a second pin, a third pin, a fourth pin, and the fan is electrically coupled to the first pin, the second pin and the third pin at least. The fan detection method includes following steps: controlling a switch to selectively conduct the first pin and the second pin; controlling a pulse width modulation (PWM) signal processing module to output a voltage pulse to the fourth pin; detecting, by the voltage detection module, a voltage level on the fourth pin; and determining the fan to be a PWM fan when the voltage level is changed, and determining the fan to be a DC fan when the voltage level is not changed.