Abstract: According to the noise characteristic of Low Light Level(LLL) image intensifier, the background noise characteristic of LLL image intensifier theoretically was analyzed. Then the photon counting method was designed, and LLL image intensifier background noise was measured by quasi-point source low light illuminometer. On the signal-to-noise ratio measurement device of the third-generation LLL image intensifier, illuminance produced by 0.2 mm point source on the fluorescent screen was measured using quasi-point source low light illuminometer with no input. For the spatial characteristics, the illuminance value inhomogeneity was less than 1% when the phosphor screen center point acted as the center of the concentric circles. But for the temporal characteristics，after the LLL image intensifiers worked 270 min later, illuminance values of phosphor screen center point could reach a steady state. Distribution characteristic of LLL image intensifier background noise based on the illuminance both in space points and time points was analyzed，and data proof for evaluating noise characteristic of LLL image intensifier was offered.