The invention discloses a method for detecting the position of a rotor of a brushless DC motor of a sensor without position by using the neutral point voltage. The structure of a rotor of the brushless DC motor takes the shape of a projecting pole, namely, the inductance Xd on a d axis of the rotor of the motor is not equal to the inductance Xq on a q axis of the motor. By detecting the neutral point voltage of a led-out winding of a stator of the brushless DC motor, the method of the invention can calculate the position of the rotor of the brushless DC motor with an energization mode each other, and the commutating time can be determined by lagging an electrical angle of 30 degrees. The method of the invention has the advantage of simple implementation of a back-electromotive force and ischaracterized in that the method takes no account of the motor revolution of an inductance method and can better determine the position of the rotor when the rotor revolution is close to from zero tothe high speed as well as reliably and accurately commutate.