Abstract: Expandable graphite was added to APP/PER/EN system to get a new kind of EG modified flame re-tardant coating. The thermal degradation, element content in residue char, char formation rate, heat insulation property of APP/PER/EN coating and EG modified flame retardant coatings were studied by using DTA, TG, SEM, EDS and heat insulation experiment. The temperature range of chemical expanding reaction among APP, PER and EN is near to that of a physical expanding process of expandable graphite, so the two processes can have good synergic effect. Expandable graphite can greatly improve the char formation rate, antioxidation and heat stability of a char layer. Too high content of EG (≥15%) makes the char layer easily detached from the substrate. 10% EG(mass fraction) can efficiently improve heat insulation and flame retardant properties of the APP/PER/EN coating.