Abstract: The Brewster window of traditional cryogenic radiometer has a great influence on the accuracy of absolute spectral responsivity calibration of standard transfer traps. In this paper, the traditional calibration for standard transfer trap was introduced. The reasons of precision degradation due to Brewster window and its state repeatability were analyzed, based on which a novel calibration scheme was proposed. The cryogenic radiometer and standard transfer trap were assembled on a concentric orbit and manipulated by an accurately electromechanical driving mechanism. By alternately switching the two instruments into calibration optical path, the absolute calibration for a standard transfer trap against cryogenic radiometer could be carried out. The new calibration system could completely eliminate the influences caused by Brewster window, would reduce about 50% uncertainty of laser power measurement and further reduce the uncertainty during the calibration process, which is of great significance in improving the accuracy of radiometric calibration.