Combined radiation calibration method based on infrared calibration stars and internal blackbody calibration source can improve the accuracy of infrared radiation measurement of spatial object. The blackbody calibration source is located inside the infrared radiation measurement system, which is used to calibrate the responsivity of the optical system. According to the atmospheric extinction model, using astronomical aperture metering method, the atmospheric extinction and system transmittance coefficient are obtained by observing multiple infrared calibration stars with higher spectral resolution at different elevation angles. The experimental results of the verification test of 700 mm aperture ground-based medium wave infrared radiation measurement system show that, in the case of sufficient exposure of star image, the inversion error of the star irradiance of the combined radiation calibration method is better than 11%. The combined radiation calibration method is simple and low cost, which can be used to calibrate the measurement equipment on-site at any time.