To obtain a high-gray two-dimensional code on the surface of packaging aluminum, a nanosecond pulse laser is used to mark the aluminum alloy surface. Further, the effect of the marking process on grayscale and the change of grayscale are investigated. CCD industrial camera, UV-visible spectrophotometer, scanning electron microscope, and energy spectrum analyzer are used to measure grayscale and spectral reflectance and observe the morphology of sample surface before and after direct low-speed labeling and high-speed labeling and then low-speed labeling. Consequently, a consistent correspondence is found between the gray level of each sample and the change in spectral reflectivity. The grayscale of the sample surface obtained using the second process reaches 92%, and the reflectivity is reduced to 10%-17%. The cause of the change in grayscale is the antireflective structure formation on aluminum alloy, and the structure has micron furrows and absorbs many nanospherical particles and flocculants.