7 153.7cm^-1 and 7 154.3cm^-1 absorption light spectrums of H₂O vapor were chosen to measure temperature distributions and H₂O vapor concentration distributions of the combustion region of CH4/Air flat flame furnace based on Tunable Diode Absorption Spectroscopy (TDLAS) and modified Algebraic Reconstruction Technique (ART). In the numerical simulation, combustion region was described by 1 000 pixels×1 000 pixels. There were 40 laser rays cross the combustion region in orthogonal two directions. By introducing the initial distribution, we found the temperature field reconstruction relative error was less than 4.5% and H₂O vapor concentration field reconstruction relative error was less than 4% based on modified ART algorithm and cubic polynomial interpolation processing. In the experiment, 24 laser rays were used to scan the target region of CH₄/Air flat flame furnace in orthogonal two directions with rotary table and slide way. Temperature field and H₂O vapor concentration field were obtained based on modified ART algorithm and cubic polynomial interpolation. A comparison of temperature reconstruction result and thermo couple result indicates the method is effective to achieve temperature field reconstruction of the combustion region.