The thermometry based on absorption spectroscopy and developing of a temperature sensor is introduced, in which temperature is retrieved by measuring line strength ratio between a pair of absorptions of water vapor near 1.4 μm. The temperature sensor is first calibrated on a tubular furnace and then used to verify measurement results with the heating tube whose both sides are open, an average fluctuation of about 50 K is obtained at each temperature setpoint. Some new absorption lines of H2O near one absorption (centered at 7153.7 cm -1) of the selected line pair are observed during demonstration measurements for CH4/air flat flame burner. These absorption lines overlapping with 7153.7 cm-1, are not listed in HITRAN08 database while HITEMP data give absorption information about these wave number positions. But line center of the other absorption (centered at 7154.354 cm-1) in HITEMP seems different from our measurement and HITRAN database. A combination of our calibrated results from tubular furnace and line parameters of new features from HITEMP is chosen and some results measured at different equivalence ratios on the burner are shown here.