Temperature measurements are ubiquitous in combustion systems. However, the accuracy of surface temperature measurements of critical components operating in a harsh combustion gases environment is greatly affected by reflection and combustion gas radiation. In this paper, an analytical two-color pyrometry model was used to quantitatively analyze the temperature errors caused by the combination of reflection and H2O-CO2-CO-N2 mixture radiation. As the results indicate, the most significant contributors to the measurement errors are found to be the error arising from H2O-CO2-CO-N2 mixture absorption and emission for two-color pyrometer operating at long wavebands. The errors due to reflection predominate over the measurement errors measured at short wavebands. In a combustor where reflected radiation from high-temperature surrounding and hot/cool combustion gas is present, two-color pyrometry is practically inoperative as a consequence of its unacceptably large measurement error and high measurement sensitivity. When the intervening gas is isothermal and the optical distance from surface to detector is considered optically thin, the temperature error has linear growth with both the H2O-CO2-CO-N2 mixture concentration and viewing path length increasing. This linear change provides us a method of linear extrapolation to eliminate the effect of uncertain gaseous absorption and emission. The results of this work can be used as a theoretical support for the design and application of a two-color pyrometer in a gas-fired furnace.