Abstract: The spectral responsivity is one of the important parameters of detector. With the development of infrared detect technique, accurate measurement for the spectral responsivity of infrared detector becomes more and more important. The technique on how to measure the spectral responsivity of infrared detector is introduced. Based on an infrared spectral responsivity facility in the institute，the cavity pyroelectric detector is used to calibrate the relative spectral responsivity of infrared detector in several wavelengths on the facility. After repeated measurement，different results are achieved and their average is given in the paper. At last the uncertainty which influences the results is analyzed. Since the wavelength range of infrared spectral responsivity facility is 1～20μm, the relative spectral responsivity of InSb detector and HgCdTe detector can also be measured. The analysis of the uncertainty shows that the measurement accuracy of the spectral responsivity of infrared detector meets the requirement.