Passive Fourier transform infrared (FTIR) technology has the advantages of remote operation, on-line analysis and no need for infrared light source etc. Based on the technology, the theory and method of calculating concentration of carbon monoxide (CO) gas at high temperature during combustion in rolling furnace of steel are analyzed. Aiming at the situation that radiation spectral measurement of heating furnace consists of two-layers homogeneous infrared radiation transfer medium, a method of changing the infrared radiation of remote sensing background by temperature control on the outside wall of furnace is proposed to obtain the characteristic spectrum of CO in furnace. Based on the combustion condition in rolling process, CO concentration simulation and analysis are carried out, and the effects of CO temperature measurement error on accuracy of measurement concentration inversion are discussed. The reference data and technical scheme are provided for the practical application of this technology.