Surface　feature　of　ammonium　polyphosphate　is　modified　by　cation　exchange　reaction　with　piperazine,　and　then　reduced　graphene　oxide　nanosheets　are　attached　to　the　surface　of　modified　flame　retardant　via　hydrogen　bonding　interactions.　Good　dispersion　of　graphene　in　the　polypropylene　matrix　is　observed.　The　dispersion　state　of　graphene　has　an　abnormal　effect　on　the　flammability　results　under　small　flame　and　fire　behavior　under　forced　flaming　condition　of　intumescent　flame　retardant　(IFR)　composites.　The　well-dispersed　graphene　results　in　significantly　deteriorated　limiting　oxygen　index　and　UL-94　rating.　The　graphene　with　good　dispersion　is　adverse　to　flammability　results,　which　is　in　contrary　to　the　widely-acknowledged　flame　retardant　mechanisms.　Low　content　of　well-dispersed　graphene　exhibits　higher　reduction　effect　on　heat　release　than　that　of　poorly-dispersed　counterpart.　Novel　flame　retardant　mechanism　and　model　are　proposed　and　new　understanding　of　the　role　of　graphene　in　the　combustion　of　IFR　is　provided.　©　2018　Elsevier　Ltd