Abstract: Using the combination of blackbody and collimator is one of the important means for infrared radiation calibration. However, due to the presence of thermal radiation, stray radiation nosie will be transmitted to the detector, generating calibration error and affecting calibration accuracy. In this paper,the stray radiation theoretical model of collimator was established, and the stray radiations of mirror surface under different working temperatures or surface emissivities were analyzed quantitatively to determine the impact on infrared radiation calibration. At the same time, some corrective measures for stray radiation were given to remove the impact on the infrared radiation calibration caused by stray radiation and improved the infrared radiation calibration accuracy.