Abstract: The reinforced aluminum matrix composites with 15vol%, 20vol%and 25vol%SiC particles were prepared by powder metallurgy method. Then, the non-destructive testing of composite materials was carried out by ultrasonic testing method, and the microstructure of defects was analyzed by metallographic microscope.The acoustic attenuation coefficient of SiC/Al composites with different volume fraction was measured and calculated by ultrasonic method. The results show that, Al line defects exist in aluminum matrix composites, and the equivalent size of defects is smaller than the actual size of defects. At the same ultrasonic testing frequency, the sound attenuation of the composite increases with the increase of SiC content. As the volume fraction of the SiC remains constant, the acoustic attenuation of the composite increases with the increase of ultrasonic test frequency.