In infrared radiation temperature measurements of wide-dynamic, high-resolution and wide-spectrum, Fourier Transform infrared (FTIR) spectrometer is a commonly used measurement unit. The nonlinearity of the spectral responsivity is one of the main uncertainty contributions to wide dynamic infrared spectrum measurements of radiation sources. Based on the flux superposition principle, nonlinearity measurement system of FTIR spectrometer measurement system was established. The experimental research on the drift characteristics of the blackbody radiation source and FTIR spectrometer measurement system during the representative nonlinearity measurement time were carried out. The quasi-linear drift effects on the nonlinearity measurement were eliminated by permuting the aperture measurement order. The nonlinear characteristics of FTIR spectrometer measurement system were experimentally measured at 200~1 000℃. The nonlinearity measurement results and associated uncertainties at 3.9 μm and 10.6 μm are reported respectively.