Properties and microstructure of recycled SBS modified asphalt were contrastively studied by the methods of infrared spectroscopy, SHRP test and four kinds of recycling agents in equal proportion were added to the aged SBS modified asphalt base on infrared spectroscopy to compare recycling agent of ZZ, RA 2, DN100, DN101, and the mechanism of SBS modified asphalt recycling is explained by use the interfacial activity theory from molecular perspective of kinematics, which show that when recycling agent is added, a layer of “interface” between asphaltene and soft asphalt is formed, macromolecule polymer or chain segment movement are accelerated, lubricated and solubilized, so that the aged asphalt viscosity decreases, the rheological properties is restored, the low temperature deformation ability is enhenced.