Abstract: The infrared radiation characteristic is an important basis for detection and identification of dim target. The acquisition of the infrared radiation characteristic of dim target needs to utilize the large diameter calibrated equipment. Spatial filter IR spectrometer can be utilized in the observation of dim target. A radiant calibration method was studied in this paper which could be applied in large diameter IR spectrometer calibration system. With this method, the radiant existance of channels around the aperture of the spectrometer measuring system was calculated according to the standard multispectral infrared radiation supplied by the combination of blackbody and collimator tube, and it was applied into the calibration of long, short and medium wave infrared. The calibration curve was fitted with the least square method and the actual calibration result was presented. The origin and combined result of calibration uncertainty was analyzed, the combined calibration uncertainty was below 10%, which met the calibration requirement of large diameter spectrometers.