A new method to detect carbon isotope ratio of carbon dioxide is presented, which is developed based on Fourier transform infrared spectroscopy (FTIR)technique. The method to obtain the absorption coefficient from HITRAN is introduced in detail. The nonlinear least square algorithm to determine δ13CO2 value is studied. The total system and experimental procedure are shown in the paper. The temperature and pressure effect on δ13CO2 value determination are analyzed from both theory and experiment analysis. For the same CO2 standard gas, the δ13CO2 value is detected by both FTIR and IRMS technology, and the results are also comparatively analyzed and discussed. The difference in mean between both methods is only 0.25%. The experimental results show that the FTIR technique to detect carbon isotope ratio of carbon dioxide is viable.