Abstract: Luminance gain, which was directly affect the image quality of night vision system in low light level condition, was an important technological index to evaluate the ability to amply image light intensity. In order to improve the repetitive characteristic of image intensifier's luminance gain, changing process of light source color temperature, light source output luminance and screen luminance had been studied respectively, theory of light source color temperature, light source output luminance and screen luminance impacting on luminance gain had been analyzed. The conclusion with warming-up of light source should not be less than 15 minutes and work time for image intensifier should not be less than 1 minute had been established. Test result showed that repetitive characteristic of image intensifier was better than 3% when light source had been warmed-up sufficiently and image intensifier's work time was controlled strictly.