Flame　retardant　modification　of　leaf　fibers　was　carried　out　to　solve　the　technical　problem　of　poor　fire　resistance　of　plant　fibers　and　improve　the　utilization　rate　of　urban　fallen　leaves　in　building　materials.　The　modification　scheme　adopts　three　flame　retardants,　i.e.,　ammonium　polyphosphate　(APP),　magnesium　hydroxide　(MH),　and　aluminum　hydroxide　(ATH),　and　two　covering　layers,　i.e.,　pure　acrylic　polymer　lotion　and　water　glass　(Na2O　center　dot　nSiO(2))　solution.　The　modified　leaf　fiber＇s　combustion　behavior　and　pyrolysis　properties　were　tested　and　analyzed.　The　physical　and　mechanical　characteristics,　as　well　as　the　thermal　insulation　qualities,　of　leaf　fiber　cement-based　composites　(LFCC)　were　studied　at　high　temperatures.　The　findings　revealed　that　the　three　flame　retardants　had　an　effect　on　the　chemical　structure　of　leaf　fibers.　In　comparison　to　leaf　fibers　without　flame-retardant　modification,　flame-retardant-modified　leaf　fibers　have　a　much　greater　thermal　stability.　and　its　LOI　is　greater　than　27.0%,　which　is　a　fire-retardant　material.　Except　for　the　sample　with　water　glass　as　the　modified　cover　layer,　at　high　temperatures,　the　composite　flame-retardant　fiber　LFCC＇s　mass-loss　rate　is　lower　compared　with　fibers　without　flame-retardant　modification　or　fibers　modified　with　only　one　kind　of　flame-retardant.　In　the　composite　flame-retardant　modified　fiber　LFCC,　the　samples　with　better　strength　at　high　temperature　are　those　with　ATH　replacing　30%　and　50%　MH.　The　thermal　conductivity　of　LFCC　is　negatively　correlated　with　the　range　of　temperature　change.