Abstract: The acoustic parameters of Pb alloy cast were tested. The results showed that the longitudinal wave velocity in the cast was relatively low and its attenuation coefficient was high, so it belonged to strong attenuation material for ultrasonic testing. The testing results of the flat-bottomed hole equivalent blocks with different diameter were analyzed, and it showed that  1 mm defect in the plate with 10 mm thickness could be detected by immersion testing or direct contact method. Thus ultrasonic testing could be used to test Pb alloy cast of moderate thickness. However, the selection of appropriate testing method to achieve best sensitivity was a key problem.