A nonlinear calibration model based on the spectral responsivity of FTIR spectrum measurement system was established. Based on the three-stage high-temperature blackbody radiation source, the spectral responsivity calibration experiment of FTIR spectroscopy system was studied. The three-stage high temperature blackbody covers 600~950 °C temperature zone, and the spectral range covers 3~14 μm. Compared with the traditional piecewise linear calibration method, the results show that the average deviation of spectral radiance and theoretical spectral radiance based on nonlinear calibration is better than 0. 04%, and the average deviation of piecewise linear calibration is 0. 93%. The two have good consistency, and the accuracy of the nonlinear calibration method is an order of magnitude higher than the accuracy of the piecewise linear calibration method.