As the existing radiation calibration for a shortwave infrared system with large aperture needs a huge infrared collimator and has poor motility and cost much, this paper proposes a new calibration method based on the amendment of inner and outer calibrations. This method sets a middle-high temperature cavity blackbody in the infrared system. By switching a mirror, it introduces the blackbody radiation into the infrared system to implement the inner calibration on parts of system at the middle-high temperature range. Then it uses a huge area blackbody to implement the outer calibration on the whole system at middle temperature range. The inner and outer calibration data at the common temperature range are picked up to calculate the amendatory coefficient in whole system. Finally, the radiation calibration data for whole system at the middle-high temperature range are captured by amending the inner calibration data. With this method, an Φ400 mm infrared system is calibrated, and the luminance error and temperature error are inverted based on the calibration results. The results show that the maximal luminance error is 1.67% and the maximal temperature error is 1.02 ℃. The results indicate that the proposed method is precise and effective for the radiation calibration of shortwave infrared systems with large apertures.