Abstract: The major types of defects of seamless steel tubes are analyzed.The automated ultrasonic testing (AUT)method is adopted to detect defects on seamless steel tubes.The detecting method, the probe arrangement, the detecting gate settings, the design of reference blocks and the display of testing results are studied.The analysis shows that the AUT method can guarantee a 100%detecting coverage of the longitudinal, transversal and layered defects on all directions of a seamless steel tube and display in real time the positions and distributions of the defects in each detecting channel.The testing results can be permanently recorded so as to realize the permanent storing and retrieving of the AUT detecting results.