Abstract: By optimizing conditions experiments of styrene-butadiene-styrene block copolymer (SBS) content, cosolvent type and dosage, processing temperature, processing time, the radiation dose rate and absorbed dose, the preparation methods of SBS modified asphalt, ⁶⁰Co irradiated SBS and irradiation SBS modified asphalt have been studied; by testing the performance index of modified asphalt cement it is to evaluate the preparation methods. The experimental results show that the mass fraction of SBS is 15%20%, the mass fraction of cosolvent is 15%-30%, blending, then at 100-165 ℃, 100-200 r/min mechanical agitation 20-30 min, at 180-210 ℃, 100-200 r/min mechanical agitation 90-140 min; or at 120-160 ℃, 100-200 r/min mechanical agitation 80-100 min, in these conditions the modified asphalt cement is better; the asphalt cement modified by SBS which was irradiated by gamma rays from a ⁶⁰Co source in vacuum at 0.75 kGy/h, 30 kGy have good performance.