Each gas has its own unique spectrum lines. The intensity of the light passing through gases decreases following the Beer-Lambert law. This enables us to predict the density of the gases as well as its temperature. Recent advent of the tunable lasers enabled us to measure simultaneous temperature and concentration fields of the gases. In this study, a numerical prediction method in which the temperature and concentration fields of the H2O vapor gas are calculated is proposed. ART (Algebraic Reconstruction Technique) method and MART (Multiplicative Algebraic Reconstruction Technique) method were tested for the prediction. The data of the Harvard HITRAN table in which the thermo-dynamical properties and the light spectrum of the H2O are listed were used for the numerical simulation. The reconstructed temperature and concentration fields were compared with the original HITRAN data, through which the constructed method is validated. It was verified that the results obtained by MART method showed relatively better agreements with those of original data.