P-N-B　organic　flame　retardant　was　synthesized　using　4-formylphenylboronic　acid,　4-aminophenylthiophenol,　9,10-dihydro-9-oxa-10-phos-phaphenanthrene-10-oxide　(DOPO),　and　then　introduced　into　the　hydroxyl-terminated　polybutadiene　acrylonitrile　(HTBN)　molecular　chain　to　successfully　prepare　a　macromolecular　flame　retardant,　which　was　used　to　prepare　flame　retardant　waterborne　polyurethane.　The　mechanical　properties,　thermal　properties,　and　flame　retardancy　of　waterborne　polyurethane　(FR-WPU)　were　studied　using　thermogravimetic　analysis　(TGA),　limiting　oxygen　index　(LOI),　scanning　electron　microscope　(SEM),　cone　calorimeter,　and　universal　testing　machine,　respectively,　and　the　flame　retardant　mechanism　of　macromolecular　flame　retardants　was　explored.　An　LOI　value　of　29.76%　and　a　UL-94　V-0　rating　could　be　realized　when　the　APFBH　conjugation　is　7.5　wt%,　showing　a　significant　improvement　of　melt　dripping　behavior　and　flame　retardancy.　It　indicated　that　the　fire　resistance　of　FR-WPU　remarkably　improved　and　displayed　both　gas　and　condensed　phase　mechanism.　As　the　content　of　APBDH　increased,　the　tensile　strength　and　the　elongation　at　break　of　FR-WPU　increased　firstly　and　then　decreased.