In this paper, a method of measuring gas temperature, velocity, and mole fraction of H₂O in a high-speed field based on near-infrared absorption spectra of H₂O is proposed. The method is applied to a supersonic combustion field and some phenomena and laws in the combustion field are analyzed. The experiment is performed in a scramjet isolation section and extended section based on wavelength modulation spectroscopy using two H₂O absorption spectral lines, and synchronous measurements of multiple parameters are realized. After performing the ignition test under combustion, the measured velocity, temperature, pressure, and mole fraction of H₂O are consistent with the predicted values when there is no shock wave in the isolation section, and the relative errors are less than 3.0%, 7.2%, 8.2%, and 3.9%, respectively. If the isolation section has a shock wave, the gas velocity, temperature, pressure, and mole fraction of H₂O have considerable differences. Additionally, information about the air mass flux has a small difference, but the fluctuation considerably increases. The experimental results show that the sensor based on wavelength modulation spectroscopy has great engineering value.