Tunable diode laser absorption spectroscopic (TDLAS)technology applies the wavelength tunable characteristics of diode lasers to the absorption spectroscopy of the selected absorption line.Based on the absorption line of water vapor，combined with HITRAN database，the frequency is chosen which fits the current environment (7181.1558cm-1)，experiment equipments are set up，the according frequency shift of the chosen frequency is measured and the fluid velocity is calculated.Experiments results show that velocity measurement is 563.06m/s，with the linear error of 5.09%，which builds good foundation for the next series of experiments under transient environments of high velocity such as shock tube.