Abstract: In recent years, ultrasonic testing artificial crack in high speed railway hollow axle increased depth mode in addition to the original chord mode. In addition, ultrasonic testing starting detection sensitivity is different between different hollow axle manufacturers. In this paper, through lots of research work on these two problems, the author found the manual crack were equivalent between chord mode and depth mode; in certain angle probe, different crack depth had the same sensitivity. It is better to use 38° angle probe to detect the fatigue crack of hollow axle.