Abstract: Signal-to-noise ratio (SNR) is an important parameter of image intensifiers, which determines the detection range and image quality of the photoelectronic imaging systems operating in low-light-level condition. On the basis of SNR chain theory of linear systems, the theoretical limiting SNR of the low-light-level image intensifier was analyzed by the noise factor expression of the system. The expression of maximum SNR for the photocathode quantum efficiency η is given in the precondition of no additional noise in each part of the system, that is NF=1, or in the ideal condition being restricted only by input photons and noise caused by the fluctuation of photoelectron quantity. The theoretical limiting SNR of the tube is ≤ 64, which is derived under the limiting condition of η=1.