In order to study the influence of ultraviolet (UV) aging on the microstructure of asphalt, this paper conducted four component, infrared spectrum and nuclear magnetic resonance tests on four kinds of asphalt respectively, and studied the changes of the four component, characteristic peak, functional group and molecular structure indexes of asphalt under ultraviolet aging, such as hydrogen spectrum, carbon spectrum, hydrogen content, molecular structure parameters and other molecular structure indexes. The influence of molecular structure change on the chemical composition of asphalt was analyzed through the characterization of molecular structure index to chemical composition index. The results show that asphaltene molecules tend to form after ultraviolet aging, and asphaltene conversion source is mainly aromatic fraction, and the higher the content of asphaltene, the higher the loss rate after aging. At the same time, the carbonyl group and sulfoxide group increase rapidly first and then flatten out with the aging time. The carbonyl group index can represent the aging of asphalt, while the sulfoxide group index can evaluate the anti-aging ability of asphalt. Under ultraviolet aging, the degree of condensation, the increase of cycloalkyl substituents, the substitution of hydrogen and the structure dissimilation of asphalt aromatic ring occur. At the same time, high UV photon energy can also cause fatty carbon to break bonds, which can improve the chemical stability of the fatty carbon connected to the aromatic ring. It can be seen from the characterization analysis that the chemical composition of asphalt is mainly affected by aromatic structure, branching degree and condensation index of aromatic ring system.