Abstract: The ultrasound velocity of longitudinal wave of NiTi shape memory alloy(SMA) had been determined by pulse-echo method and the ultrasound velocity was measured at different temperature. The results show that the ultrasound velocity varied slowly with temperature if no phase transformation was induced, but sudden change in the ultrasound velocity could be observed when phase transformation occured. The phase transformation temperature determined by the ultrasound velocity method had a good consistence with that of the traditional electric resistance method. It could be concluded that the ultrasound velocity method with the advantage of operating conveniently, no damage to parts and so on could be used to examine phase transformation of SMA.