To　improve　the　properties　of　styrene-isoprene-styrene　(SIS)　modified　asphalt　and　decline　the　SIS　content　in　asphalt　further,　SIS　compound　modified　asphalt　has　been　prepared　by　the　addition　of　SIS,　polyphosphoric　acid　(PPA)　and　sulfur.　The　physical　and　rheological　properties　of　modified　asphalts　were　studied　and　the　structural　characteristics　were　analyzed　by　adopting　morphology　observation,　infrared　spectroscopy　and　thermal　analysis.　The　research　showed　the　suitable　addition　of　PPA　improved　the　high-　and　low-temperature　properties　of　asphalt　and　declined　the　SIS　content　without　negative　effect.　The　use　of　sulfur　can　improve　the　storage　stability　of　modified　asphalt　greatly　and　increase　the　susceptibility　to　ageing.　The　morphology　and　infrared　analysis　indicate　the　effects　of　PPA,　sulfur　and　ageing　on　the　structural　characteristics　of　asphalt.　The　calculation　for　the　characteristic　peaks　of　enthalpy　curves　in　thermal　analysis　was　used　to　investigate　the　influence　of　PPA　and　sulfur　on　the　distribution　of　molecule　weight　and　constitutes　of　SIS　modified　(SM)　asphalt　before　and　after　ageing　efficiently.　©　2017　Elsevier　B.V.