The temperature, H2O concentration, pressure, velocity and mass flux of supersonic gas flow are measured based on scanning wavelength-modulation spectroscopy method. The simultaneous measurement methods of multiple parameters of supersonic gas flow in uniform flow filed are studied using the harmonic signals of two H2O absorption spectral lines. The measurement results based on wavelength modulation spectrum technology can precisely reflect the gas parameters in the uniform flow field, while the actual flow field often has the boundary layers. Aiming at the approximate uniform flow field with boundary layer, the numerical simulation is carried out to study the effect of line selection and boundary layer thickness on the measurement result of core flow in flow field. The simulation results show that the measurement error increases with the boundary layer thickness, and the absorption spectral lines which are insensitive to temperature of boundary layers can effectively decrease the influence of boundary layer. The experiments of supersonic gas flow is carried out in a direct-connected scramjet test facility isolator, the results show that the measurement method based on wavelength modulation spectroscopy has high measurement accuracy in strong noise and strong vibration environments. The maximum relative deviation of predicted value and measured value for temperature, H2O concentration, pressure, velocity and mass flux are less than 8.2%, 7.2%, 2.0%, 3.1% and 6.4%, respectively.