Abstract: Experiments were performed by X-ray, CT and ultrasonic methods on the defects which were detected in SiC_p/Al composite. Characteristics of defects were determined on the basis of metallography and NDT results. The difference between quantitative results and real sizes was analyzed. The results show that particle aggregation is one of the main defect types in SiC_p/Al composite. The quantitative results of CT are closer to the real size than that of ultrasonic testing. The study results are of great reference value to the quality control of SiC_p/Al composite components.