Abstract: To investigate the SBS(styrene-butadiene-styrene) swelling characteristic and its impact on service performance,14 groups of SBS modified asphalt samples at 3 dosages were prepared by adopting4 kinds of SBS and 3 kinds of base butimen.And the samples were observed and taken pictures by fluorescence microscopy.By using some of MATLAB functions,the SBS area ratio was calculated in fluorescence microscopy images and the relationship between SBS area ratio and raw materials was analyzed.The impact on equivalent softening point,equivalent brittle point,penetration index,plastic temperature range of SBS area ratio was researched.The results show that star-shaped SBS has larger SBS area ratio than linear SBS in modified asphalt.Different base asphalt shows different SBS area ratio.The SBS area ratio is increasing with the SBS content.With the SBS area increasing,the high temperature performance of modified asphalt increases,but there is no apparent regularities of the temperaturesensitive and low temperature stability.The SBS modified asphalt shows better pavement performance when SBS area ratio is at the range between 31.26%and 36.16%.The result provides a reference for improvement of quality control index for SBS modified asphalt in microscopic field.