Abstract: Low-light-leve (LLL) image intensifier is the core component of LLL imaging technology, signal-to-noise ratio(SNR) of image intensifier is one of the important parameters of image intensifier, which is quantitative characterization of image intensifier performance in the detection of weak radiation image, and can reflect the influences of space factor and time factors on the detection of image features. SNR measurement principle and devices of LLL image intensifier were introduced. The measurement device adopted precise microporous grating, variable grating and conjugate symmetric lens system, and could realize that a diameter of 0.2 mm particular spot projected onto the cathode surface of image intensifier. Adopting photon counting technology, by studying the weak light intensity calibration method on small detection surface (probe diameter less than 4 mm), the accurate calibration of pinhole weak illumination and the accurate measurement of light source illumination SNR with diameter of 0.2 mm were solved.