Calibration to standard reference gas scale is necessary to improve the accuracy of the measurements，and ensure the compatibility of measurement values between different instruments for δ¹³CO₂ value based on Fourier Transform Infrared(FTIR) spectroscopy. Firstly, the calibration methods were put forward, the absolute calibration and empirical calibration methods were studied in detail. On the basis of these researches, the δ¹³CO₂ values were calibrated to standard reference gas scale. The calibration results show that measurements accuracy has been improved greatly, compared with measurement results of no calibration. The accuracy for absolute calibration and empirical calibration methods are improved 5.5 and 6.4 times respectively. The study is benefit to improve the accuracy of FTIR measurements and the compatibility between different instruments.