Organically　modified　ammonium　polyphosphate　(APP)　flame　retardant　is　prepared　by　supramolecular　assembly　method　using　melamine　formaldehyde　(MF)　resin　and　phytic　acid　(PA)　as　building　blocks.　Surface　characteristics　of　APP　are　modified,　resulting　in　the　enhancements　in　water　resistance,　dispersion　in　the　polymer　matrix　and　their　compatibility.　This　supramolecular　assembly　modified　APP　(APP@MF-PA)　matches　well　with　charring-foaming　agent　(CFA)　to　achieve　excellent　fire　safety　for　polypropylene　(PP),　and　the　superiority　over　conventional　APP　is　observed.　Heat,　CO　and　CO2　releases　of　PP　are　greatly　decreased　by　the　intumescent　flame　retardant　(IFR)　formulation　containing　APP@MF-PA　and　CFA.　The　modification　of　APP　with　MF-PA　supramolecules　are　beneficial　to　improve　the　yield,　insulation　properties,　graphitization　degree　and　compactness　of　char.　Flame-retardant　mechanisms　are　demonstrated　according　to　the　investigations　on　gaseous　and　condensed　phase　products.　This　novel　and　facile　modification　method　provides　a　new　strategy　for　improving　the　flame-retardant　efficiency　of　IFR.