In order to make up for the deficiency of SBS modified asphalt in application. The physical property test, rheological property test and micro analysis of PU / SBS modified asphalt with different content were carried out to explore the change law of composite modified asphalt. The results show that the three indexes of composite modified asphalt could be improved, the viscosity of SBS modified asphalt also would be increased, and enhanced the rutting resistance and high temperature stability of asphalt, but the improvement of low temperature performance was not significant. Through comparative analysis, the optimum content was 4% SBS + 6% PU.