Abstract: Eight-channel ultrasonic C-scan testing was carried out on 8mm aluminum alloy sheets. The key testing parameters affecting the test results were analyzed and validated by the comparative test block which was designed and manufactured according to GJB1580A-2004 AAA grade acceptance requirements. The results show that the detection process identified in this paper can achieve the detection sensitivity of φ0.4 mm, which can be applied to the highly efficient and automated ultrasonic testing of similar sheet metal.