Abstract: The exhaust noise radiation of APU (Auxiliary Power Unit) on MA60 aircraft is serious. Effective sound treatment technology should be employed to control the exhaust noise. The measured spectrum of APU exhaust noise shows that typical exhaust noise spectrum is very broad. Two general regions can be distinguished. A broad hump of low frequency random noise centering in the 400-1000 Hz region normally is present, which often is substantially stronger when fully loaded. A second broad hump of high frequency random noise centers in speech interference region of 1000-5000 Hz,which is the frequency range of the ear's greatest acuity. Considering the measured spectrum and APU equipment,a microporous muffler is used for reducting of APU exhaust noise. The measured results show that the effect of microporous muffler for noise reduction of APU exhaust is very satisfactory.