The High-spectral Infrared Atmospheric Sounder II (HIRAS-II) is a Fourier transform spectrometer onboard the world’s first civil early-morning-orbiting FengYun 3E (FY-3E) meteorological satellite, the FY-3E/HIRAS-II focus on a number of upgrades such as the sensitivity of the detector, the accuracy of spectral calibration and radiometric calibration, with the designed and manufactured processing based on the first Chinese hyperspectral infrared (IR) sounder FY-3D/HIRAS-I. We conducted a comprehensive pre-launch thermal vacuum (TVAC) calibration tests for HIRAS-II, including the nonlinearity (NL) correction which consists an essential part of radiometric calibration, the NL correction has considerable effects on radiometric accuracy. According to the HIRAS-II nonlinear behavior of the detectors for long-wave (LW) and mid-wave1 (MW1) infrared spectral bands, the NL correction of raw data in the spectral domain is a scaling of the observed spectrum, the NL correction coefficients are derived by the methods of minimizing the spread of the responsivity of reconstructed spectrum in each wavenumber with varying temperature, or minimizing the spread of the bias of brightness temperature among calibration targets with varying temperature. The bias of spectral brightness temperature is assessed by comparing the NL correction and the non-NL correction radiometric calibration data, the results show that, the radiometric accuracy has been significantly improved via NL correction.