In order to study the molecular weight and molecular structure changes of asphalt under ultraviolet aging and the mechanism of their effects on macro properties, gel permeation chromatography and nuclear magnetic resonance tests were carried out on four commonly used asphalt, respectively. The molecular weight composition changes, such as molecular weight and molecular relative mass distribution, and the molecular structure composition changes, such as hydrogen spectrum, carbon spectrum, hydrogen atom content and molecular structure parameters were studied. On the basis of macroscopic rheological tests, the molecular composition of asphalt rheological properties was characterized by correlation analysis, and the molecular mechanism of ultraviolet aging macroscopic properties was analyzed. The results showed that ultraviolet aging caused the agglomeration of molecules in asphalt, small molecules decreased and aggregated into large molecules, and the molecular weight distribution boundary narrowed gradually. From the changes of hydrogen atoms and molecular structure parameters, it can be seen that the alkyl substituents on the aromatic ring in the asphalt increase after ultraviolet aging, resulting in the increase of the volume and stability of the aromatic ring, and the increase of molecular backbone stiffness. On the macro level, the elastic properties of asphalt increase. The phase Angle, rutting factor, irrecoverable compliance and recovery rate of asphalt before and after ultraviolet aging were obtained by macroscopic rheological tests. The correlation analysis showed that the rheological properties were most affected by condensation degree parameters, substitution rate of peripheral hydrogen, average molecular weight and branched degree of alkyl chain.