Abstract: In view of problem that it is hard to precisely measure time of pulse arriving at receiving sensor due to presence of start-up process when ultrasonic sensor receives ultrasonic pulse signal, the paper proposed a method of precise measurement of air speed in mine ventilation. The method fits the curve and envelope curve of sinusoidal signals received by receiving sensor, and calculates time of the ultrasonic pulse signal arriving at the sensor. The results of calculation and analysis of simulate sampling data show that the method can achieve high measuring precision, which can improve measurement accuracy of mine tunnel air speed.