The maximal visual range of low light level (LLL) imaging apparatus is a basic guideline in system's design. Based on the early work, the visual range equation of LLL imaging system has been summarized. The laser aids system is used in order to improve its watching ability in bad weather. If so, there would be changed in the equation of visual range, especially the spectral matching factor. What's more, the illumination, contrast, reflectivity and so on would be changed. The changes about these factors after the adding of the laser are discussed, which can help choosing the lasers. The visual range of the super second generation image intensifiers under the laser aids is estimated, which proved the laser (λ=850 nm) is reasonable.