Abstract: An ultrasonic testing model for the volume fraction of SiC and porosity in SiC particle reinforced aluminum matrix(SiC_p/Al) composite was established through theoretical analysis, which was based on the ultrasonic velocity of longitudinal wave. SiC_p/Al composite samples with SiC volume fraction of 10%, 15%, 20%, 25%, 30% were prepared by powder metallurgy process respectively. The velocity, SiC volume fraction and porosity of those samples were measured, then an experimental relation curve between measured velocity, SiC volume fraction and porosity was established. And finally, the SiC volume fraction of another SiC_p/Al composite sample with a nominal volume fraction of 20% was calculated using the experimental relation curve. The results indicate that the experimental relation curve is in good agreement with the theoretical prediction curve calculated by the model, the relative error of the SiC volume fraction evaluated by ultrasonic method is 5.2%, which proves the feasibility of this method. The research considers the effect of porosity while detecting the SiC volume fraction, which provides a new idea for nondestructive evaluation of metal matrix composites.