In order to explore the aging mechanism of leather relics under the influence of light, in this study, we used artificially-aged modern vegetable-tanned sheepskin as the simulation samples, and carried out Fourier transform infrared spectrometry, scanning electron microscopy, atomic force microscopy, colorimetric analysis and thermogravimetric analysis to explore the micro and macro changes in the aging process of the samples. The results show that light caused the oxidation of amino acids and tannins in leather, seen by the appearance of a characteristic carbonyl peak at 1 715 cm-1. The carbonyl index increased with the extension of light time and thus could be used as a quantitative index of the degree of leather oxidation. Oxidation of aromatic amino acids and vegetable tannins could cause leather discoloration, and a prediction model of color difference changing with light time could be obtained by fitting. When the hydrogen bonds broke under the action of light, the intramolecular random curling content of collagen increased to 33.14%. This proved the unwinding of the triple helix structure of collagen, an increase of molecular disorder, a decrease of stability, and the release of part of the crystalline water. In addition, the moisture and lipids in the leather were lost under the light, which made the fibers shrink and curl, and the gap between fibers increased. At the same time, stress was generated, which gradually accumulated and caused the deformation of the leather surface.