Abstract: In this paper, a portable phased array ultrasonic device and two linear array transducers with different geometric parameters are utilized to detect the 6 mm and 9 mm defects in a carbon fiber composite laminate. Non-focusing linear scan and focusing linear scan are adopted, respectively, and C scan image is shown to study and analysis. The experiment reveals that in the case of non-focusing linear scan, the accuracy of the size of defects has a close relation with the lengths of the element and aperture. The experiment results show good agreements with theoretical analysis; but in the case of focusing linear scan, the accuracy of the defect size is not affected by the overlarge aperture.