Epoxy　resin　(EP)　is　widely　used　in　various　industries.　However,　its　inherent　flammability　characteristics　limit　its　application,　so　there　is　an　urgent　need　to　develop　bio-based　flame　retardants　for　efficient　flame　retardant　EP.　Chitosan　(CS)　is　one　of　the　most　commonly　used　bio-based　raw　materials,　but　most　chitosan-based　flame　retardants　are　synthesised　using　large　amounts　of　organic　solvents,　with　low　yields　and　not　in　line　with　the　theme　of　green　and　sustainable　development.　In　this　paper,　we　report　a　facile,　eco-friendly,　and　solvent　-free　approach　to　chitosan-based　flame　retardants.　A　novel　full　biomass　flame　retardant,　chitosan-based　ammonium　phytate　(PUCS),　was　synthesised　without　the　organic　solvent　by　using　chitosan　and　phytanic　acid　as　raw　materials　and　the　electrostatic　adsorption　interaction　between　them　and　urea,　and　it　was　used　as　a　flame　retardant　additive　for　EP.　The　results　showed　that　the　EP　samples　with　7.5　wt%　PUCS　added　increased　the　limiting　oxygen　index　from　22.2　%　to　32.2　%　and　the　vertical　burning　rating　from　no　rating　to　V-0.　Moreover,　the　cone　calorimeter　test　results　showed　that　the　EP/PUCS　composites　with　adding　PUCS　showed　a　significant　decrease　in　the　peak　heat　release　rate,　and　it　has　excellent　flame　retardancy.　It　is　worth　mentioning　that　the　mechanical　property　test　results　showed　that　the　mechanical　properties　of　EP/PUCS　composites　with　adding　PUCS　could　still　reach　the　scope　of　the　needs　for　engineering　applications.　This　work　provides　an　economical,　convenient,　and　eco-friendly　feasible　route　for　bio-based　flame　retardants.