Abstract: Extraction of instantaneous velocity in doppler echo signal is of great significance to the analysis of target motion state. However, general analytical methods can not provide sufficient time-frequency focusing performance due to the restriction of nonstationarity. A method based on generalized S transform （GST） was suggested to extract instantaneous velocity from the ultrasonic doppler signal, and computer simulation and experiment verification were carried out. In the simulation, a model system was set up, which contains a reciprocating dot. The doppler echo signal was produced by transmitting ultrasonic waves to the reciprocating dot. In the experiment a machinery device with reciprocating movements was designed, which gets echo signal by transmitting ultrasonic waves. The instantaneous frequency was obtained by processing the echo signal with GST and the instantaneous velocity was calculated. The computer simulation and experiment demonstrate the effectiveness of extraction of instantaneous velocity of the moving target in the doppler echo signal by GST.