The accuracy of quasi-homogeneously heated gas temperature measurements in the range of 1500-2100 K using the developed line-of-sight gas flow thermometer, based on diode laser absorption spectroscopy (DLAS) of H2O molecules, has been experimentally verified. As a test object, a laminar partially-premixed methane-air flame of a slot burner has been employed, which was providing high homogeneity of the temperature distribution along the slot. The average temperature values obtained using DLAS in the line-of-sight measurements along this direction in various parts of the flame are compared with the results of local temperature measurements along this line carried out using coherent anti-Stokes Raman spectroscopy (CARS). Absolute values and profiles of temperature determined using DLAS are in a reasonable agreement with the results of CARS-measurements, and the differences at temperatures of ∼ 1500-2100 K do not exceed 10%.