In order to effectively measure gas flow rate in wind tunnel, based on the principle of laser Doppler frequency shift, combined with wavelength modulation tunable diode laser absorption spectroscopy (TDLAS) technology, using HITRAN database, oxygen (O2) molecular absorption spectral line near 13144.5 cm-1 is selected as the research object. A gas flow measurement model is built in the software, the flow velocity measurement results are simulated and analyzed. Supersonic wind tunnel devices are used in the laboratory to set up a set of wavelength modulation flow measurement system based on TDLAS technology. Through the experiment, second harmonic signal of O2 is extracted. According to the second harmonic of O2 molecular absorption spectral line frequency shift, the flow velocity in the wind tunnel is reversed. The experimental results show that, in the laboratory environment, velocity measured by the system reaches 707.6 m/s. The experimental results are consistent with the supersonic wind tunnel design, and the measurement error is 5.47% . The results prepare for the research of system miniaturization, which measures flow rate based on wavelength modulation - TDLAS, and flight experiments.