In this study, an accurate absorption model is established by using the wavelength modulation technology based on tunable diode laser absorption spectroscopy. The free spectral range of an etalon is calibrated by the two absorption lines whose transition line centers are known, and the frequency-time response of the laser is obtained using a description model close to the output characteristics of the laser. Along with the hybrid absorption line parameters calibrated in the laboratory and the HITEMP database, an accurate model that can be directly compared with the actual absorption is established for diagnosing the combustion flow field. Herein, H2O is the target molecule, and the transition line centers of the two selected lines are 7185.60 and 6807.83 cm -1. The flow field temperature can be obtained via the peak of the normalized second harmonic signal with background subtracted and verified in a high-temperature flow field generated by a tubular high-temperature furnace. The maximum temperature is 1500 K, and the relative measurement error is less than 3.1%. Further, the accuracy of the absorption model determines the accuracy of the measured flow field parameters. The method used to establish the model can be applied to the complex combustion flow fields for accurately measuring the flow field parameters.