Abstract: The working principle of the image intensifier is analyzed since it has not only the special property of optoelectronic imaging but also the characteristic of spectral conversion. A new method, which takes a cavity pyroelectric detector as a reference detector to measure the spectral responsivity of photocathodes in image intensifiers, is proposed. The measurement principle of the photocathode spectral responsivity for image intensifiers is described. The calibration of allwave absolute spectral responsivity of photocathodes in image intensifiers was realized by means of the calibration of the absolute spectral responsivity at 632.8nm for a silicon photocathode by using the cryogenic radiometer of the radiation standard and the trap detector of radiation transfer standard. The highprecision and broadband instrument designed for measuring the spectral responsivity of photocathodes in image intensifiers is of benefit to the development and fabrication of photocathodes in image intensifiers.