LLL (Low-light-level) / infrared image fusion can integrate both bands information of the target, it is beneficial for target detection and scene perception in the low visibility weather such as night, haze, rain, and snow. The quality of fused image is declined, when any channel image quality drops. There will be great changes in the brightness, contrast and noise on LLL images when environment illumination has obvious changes, but the current color fusion methods is not adapted to the environment illumination change in larger dynamic range. In this paper, LLL image characteristics are analyzed under different environment illumination, and a kind of adaptive color fusion method is proposed based on the RGB color space. The fused image can get better brightness and signal-to-noise ratio under the different intensity of illumination.