Abstract: To ensure the accuracy of radiation measurement, it is necessary to calibrate the infrared radiation measurement system. Based on the analysis of working principle of infrared radiation measurement system, a calibration method combined internal and external calibration was proposed which was different from the traditional calibration method. It separated measurement system to calibration step-by-step, no longer as a whole black box. Through theoretical derivation the internal and external calibration calculated formula was given. The experiments show that the calibration accuracy of the new method is accord with traditional full-aperture blackbody calibration method, within 1% relative error. This method reduces the requirements of temperature range of the external full-aperture blackbody, also reduces the development difficulty and cost of blackbody.