The four component model of asphalt was established by Materials Studio software, and the glass transition temperature of the asphalt model was calculated by volume temperature curve. The differential scanning calormetry(DSC) test was used to prove the reliability of the glass transition temperature of the asphalt model. At a temperature below the glass transition temperature, molecular dynamics was used to simulate and analyze the physical aging of asphalt molecules from the microscopic level. The results show that under the isothermal and isobaric conditions below the glass transition temperature of asphalt, the asphalt model exhibits a physical aging phenomenon with reduced free volume and increased density over time. At the same time, asphaltene and resin at low temperatures cause physical degradation of asphalt activity, and the molecular activity of micro Brown movements mainly comes from saturated and aromatic components.