Abstract: Two kinds of silicon carbide particulate reinforced aluminum composites in which the particle size ratio of silicon carbide to aluminum alloy power is different were fabricated by power metallurgy method. The ultrasonic velocity, attenuation and grass of the two kinds of composites were researched under hot pressed status and extruded status in radial and axial direction. The results indicated that the ultrasonic velocity, attenuation and grass can be used to evaluate the microstructure of composite fabricated by power metallurgy method nondestructively. The ultrasonic velocity and grass can reflect anisotropy of composites, and the grass can also reflect the distribution of silicon carbide particle. The ultrasonic attenuation is sensitive to hot extrusion.