Aiming to investigate the influence of functional group index variations on the low-temperature performance of asphalt at different aging stages, three base asphalts (70#, 90#, and 110#) were selected as raw materials, and three common modifiers including SBS, SBR and rubber were used to prepare nine modified asphalts. First, the low-temperature thermal properties of each asphalt were tested using a thermal analyzer. Subsequently, Fourier transform infrared (FTIR) spectroscopy was employed to obtain the infrared spectra of the three base asphalts and nine modified asphalts in their original state. The 12 original asphalts were then subjected to rolling thin-film oven test (RTFOT) and pressure aging vessel (PAV) aging to simulate short-term and long-term aging, respectively. Infrared spectra were collected for the original, short-term aged, and long-term aged samples. Based on the characteristic absorption peaks in the spectra, the presence of functional groups in different asphalts at various aging stages was qualitatively analyzed. Finally, a quantitative relationship between functional group indices and the glass transition temperature (T_g) was established to evaluate the changes in functional group content during low-temperature aging. The experimental results indicate that a higher index of saturates and aromatics in asphalt leads to a more uniform distribution of asphaltene molecules within the asphalt system, resulting in a more stable molecular structure. The functional group content in asphalt undergoes significant changes at different aging stages. The carbonyl and sulfoxide indices exhibit the most substantial increase, while the saturate and aromatic indices show the greatest decrease. Asphalts with a larger reduction in saturate and aromatic indices exhibit weaker aging resistance. The aromatic index demonstrates the strongest correlation with the glass transition temperature (T_g).