The invention discloses a horn adaptive to change of width ratios and a method for adjusting sound of the horn. The horn comprises an electromagnetic coil (1). The electromagnetic coil (1) is connected with a driving circuit (2) and a mechanical sound production device (6), the driving circuit (2) is connected with an oscillating circuit (3), the oscillating circuit (3) is connected with an oscillating pulse width ratio adjusting circuit (4), the oscillating pulse width ratio adjusting circuit (4) is connected with a sensor (5), and the sensor (5) is connected with the mechanical sound production device (6). The horn and the method have the advantages that problems of possible noise and changed sound of an existing frequency-adaptive horn can be solved by the aid of the horn and the method, and the method can be applied to horns of automobiles.