To determine the influence of ultraviolet (UV) aging on the microstructure of asphalt. The four-component, infrared spectrum, and nuclear magnetic resonance tests on four kinds of asphalt respectively were conducted, and the changes of the four components, characteristic peak, functional group and molecular structure indexes of asphalt under ultraviolet aging were investigated as well, 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 the molecular structure index to the chemical composition index. The results show that asphaltene molecules tend to form after ultraviolet aging, and the asphaltene conversion source is mainly aromatic fraction. The fact is founded that the higher the content of asphaltene, the higher the loss rate after aging is. Meanwhile, 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 the asphalt aromatic ring occur. At the same time, a 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 the aromatic structure, branching degree, and condensation index of the aromatic ring system.