Abstract: The spectral responsivity of IRFPA imaging detector is a basic physical parameter for the space infrared remote sensing. In order to use this parameter to eliminate the influence of the non-uniformity on the product quality in the fabrication process, the spectral responsivity of detectors must be calibrated and the real value should be obtained before the systems are put into use. Because of the uncertainty of the calibration data-acquisition methods and the limitation of some calibration methods, the measured value is not accurate. Thus it is very important to select a proper method and to analyze its error. In this paper some methods for calibrating the spectral responsivity of IRFPA detectors were analyzed, and the limitations of the calibration methods available were investigated. The standard substitution method for the products was selected, and the possible errors were analyzed based on the obtained data. Some important issues in the calibration process of IRFPA products were summarized. An integration time adjustment method is put forward to overcome the big error caused by the low radiation rate of calibration blackbody in some wave bands.