A　styrene-butadiene-styrene　(SBS)　modified　asphalt　compound　was　prepared　by　the　addition　of　polyphosphoric　acid　(PPA)　and　sulfur.　The　effect　of　PPA　and　sulfur　on　major　physical　properties,　including　toughness　and　tenacity,　aging　resistance,　and　storage　stability　was　investigated.　The　structural　characteristics　of　SBS-modified　(SM)　asphalt,　SBS/PPA-modified　(SPM)　asphalt,　and　SBS/PPA/sulfur-modified　(SPSM)　asphalt　were　investigated　using　scanning　electron　microscopy　(SEM),　gel　filtration　chromatography　(GPC),　and　thermal　analysis.　It　has　been　found　that　acidification　prompted　the　clustering　of　SBS　particles　and　confined　the　swelling　of　SBS,　making　SPM　asphalt　more　susceptible　to　aging.　Vulcanization　changed　the　morphological　characteristics　of　SBS　in　asphalt,　improved　the　compatibility　between　SBS　and　asphalt,　and　weakened　the　aging　susceptibility.　Therefore,　it　is　reasonable　to　modify　SM　asphalt　by　using　PPA　and　sulfur　together.