Achieving　a　balance　between　flame　retardancy　and　overall　performance　in　epoxy　resin　(EP)　continues　to　be　a　significant　challenge.　In　this　study,　a　new　multi-DOPO-based　reactive　flame　retardant　(DZH)　was　synthesized　successfully　using　a　simple　one-pot　method　and　employed　as　a　co-curing　agent　with　DDM.　The　results　indicated　that　the　inclusion　of　DZH　decreased　the　activation　energy　of　the　curing　reaction　system.　Furthermore,　the　presence　of　DZH,　with　its　remarkable　charring　ability,　enhanced　the　formation　of　char　residues　under　high-temperature　conditions.　Notably,　the　flame　retardancy　and　mechanical　properties　of　the　EP/DZH　system　were　significantly　enhanced　at　certain　additions.　When　added　at　only　5　wt%　(phosphorus　content:　0.525　wt%),　the　LOI　value　of　the　EP/DZH-5　increased　from　24.4　%　to　35.3　%　for　the　EP　matrix　and　achieved　a　V-0　rating　in　accordance　with　UL-94.　Meanwhile,　EP/DZH-5　exhibited　a　reduction　of　44.1　%　in　pHRR　and　24.3　%　in　SPR.　The　superior　flame　retardancy　of　the　EP/DZH　system　was　attributed　to　the　dual　flame-retardant　mechanism　exhibited　in　both　the　gaseous　and　condensed　phases.　In　addition,　the　abundant　presence　of　rigid　phosphaphenanthrene　groups　and　π-π　interactions　between　benzene　rings　led　to　an　improvement　in　the　tensile　strength　and　tensile　modulus,　which　rose　to　91.0　MPa　and　1.76　GPa,　respectively,　from　79.5　MPa　and　1.26　GPa　of　EP　in　the　case　of　EP/DZH-3.　The　utilization　of　this　flame　retardant,　based　on　multi-DOPO,　offers　a　promising　approach　for　the　development　of　high-performance　epoxy　resins.　©　2023　Elsevier　B.V.