Abstract: Pinhole is one of the most common defects of cast aluminum alloys. The method of metallographic visual comparison of random sampling is used to evaluate the level of pinhole in modern industry. But it is time/labor consuming and affected by human factors. In this paper, the ultrasonic nondestructive testing method by collecting signals from the samples with different pinhole levels, calculating the ultrasonic longitudinal/transversal wave velocity and attenuation coefficient, summarizing the relation and variation between these parameters and pinhole defects, is used to evaluate the level of pinhole. Experiment results show that it is feasible that inspecting and evaluating the pinhole defect of cast aluminum alloys by ultrasonic nondestructive testing method. And this method is rapid, objective and accurate.