The aging mechanism of SBS modified asphalt during its aging process was studied.The characterizations of base asphalt,SBS polymer and its modified asphalt were determined in different aging time by Fourier transform infrared spectrum(FTIR).FTIR shows that oxidative dehydrogenation reaction occurs in asphalt,and unsaturated carbon bond is generated under short-term thermal aging condition.Additionally,SBS polymer was aged significantly under that condition,the speed of which was faster than that of base asphalt.The aging laws of both asphalt and SBS polymer during the aging process of SBS modified asphalt were similar to their aging laws respectively.Due to the protective effect between asphalt and SBS polymer,the aging degrees of asphalt and SBS polymer were lower than those aged independently. The aging mechanism of SBS modified asphalt during its aging process was studied. Characterizations of base asphalt, SBS polymer and its modified asphalt were determined in different aging time by Fourier transform infrared spectrum (FTIR). FTIR shows that oxidative dehydrogenation reaction occurs in asphalt , and unsaturated carbon bond was generated under short-term thermal aging condition. Additionally, SBS polymer was significantly significantly under that condition, the speed of which was faster than that of base asphalt. the aging laws of both asphalt and SBS polymer during the aging process of SBS modified asphalt were similar to their aging laws respectively. Due to the protective effect between asphalt and SBS polymer, the aging degrees of asphalt and SBS polymer were lower than those aged independently.