Abstract: For an online adaptive active noise control system based on Filtered-xLMS algorithm and by means of M senial signal, the effect of the installation angle of the secondary source on the noise attenuation in engine exhaust duct is studied. By changing the secondary source installation angle, the attenuation effect is tested on line so as to validate the validity of the theory. Finally, the conclusion is made that optimizing the installation angle can improve the noise suppression.