Basedonaself-developedreactivecoldmixedflameretardantasphalt， the flameretardant effect and mechanism of dec a bromo diphenyl ethane(DBD PE) flame retardant reac-tive cold mixed asphalt were studied.Scanning electron microscope test， infrared spectrumtest and thermal analysis test were used to study the dispersioncompatibility and_state，thermal weightloss behavior of the flame retardant in reactive cold mixed asphalt， and theflame retardant mechanism was revealed compared with the pyrolysis law of reactive coldmixed asphalt and reactive cold mixed flame retardant asphalt.The oxygen index test re-sults show that the oxygen index parameter of the reactive cold mixed flame retardant as-p halt can reach 26%.Scanning electron microscope testresults show that the flame retard-ant has good dis pens ability in reactive cold mixed asphalt.Infraredspectrumtestresults show that the flame retardant DBD PE does not chemically react with cold mixed asphalt，which is a physical blend with good compatibility between them.Thermal analysis test re-sults show that DBD PEis mainly based on the gas-phase flame retardant mechanism， butalso plays a solid-phase role.DBD PE increases the final decomposition temperature of reac-tive cold mixed flame retardant asphalt from 641.5℃to more than 800℃， and the peakvalue of heat flowrate is reduced from—22.7mW/mg to-16.7mW/mg.