Polystyrene　(PS)　composites　with　different　loading　level　and　proportions　of　CNAPP20　[i.e.,　ammonium　polyphosphate　(APP)　wrapped　graphitic　carbon　nitride　(g-C3N4),　where　mass　ratio　of　g-C3N4　to　the　CNAPP　was　20%]　to　aluminim　phosphinates　were　fabricated.　The　results　indicated　that　the　additives　had　good　interfacial　interaction　with　PS　matrix.　It　is　noted　that　only　the　PS-1　achieved　the　UL-94 V-0　rating,　and　value　of　limited　oxygen　index　was　also　the　highest　among　all　the　composites.　The　peak　of　heat　release　rate　(pHRR)　and　total　heat　release　of　all　the　composites　were　greatly　reduced　as　compared　to　those　of　virgin　PS　(77.5%　decrease　in　pHRR　for　PS-1).　Combining　CNAPP20　with　DAHPi　(i.e.,　aluminim　diethylphosphinate)　induced　the　formation　of　a　cohesive　and　uniform　carbonaceous　residue.　In　addition,　the　concentration　of　carbon　dioxide,　smoke　and　carbon　monoxide　was　reduced　upon　incorporation　of　CNAPP20　and　DAHPi.　The　property　improvements　were　attributed　to　the　explanations　that　the　formed　continuous　and　dense　char　residues　acted　as　protecting　layers　to　prevent　the　heat　and　mass　permeation,　and　that　the　evolved　gas　diluted　the　oxygen,　which　retarded　the　further　combustion　of　flammable　compounds.　Also,　the　generated　free-radical　scavengers　retarded　polymeric　chain　breakage.　©　2017,　Akadémiai　Kiadó,　Budapest,　Hungary.