Abstract: The effects of nanometerCaCOand hexaphenoxycyclotriphosphazene(POP) as a halogen- free fire-retardant on the mechanical and combustion properties of polypropylene/magnesium hydroxide(PP/Mg(OH)2)blends were studied in this paper.It showed that, when the total amount of inorganic powder kept at 90 phr, the mechanical properties of the blends increased firstly and decreased with in- creasing content ofCaCO3,with the optimum content being 40 phr.The addition of POP could reduce the loading level of Mg(OH)2 and may improve the mechanical properties and fire-retardant performance of the blends. When POP content was 8 phrelongation at breaktensile strength,impact strength and oxygen index reached 264.76%，2234MPa4865kj/m，and28.2%，respectively.

Key words: polypropylene, magnesiun hydroxide;calcium carbonate;hexaphenoxycyclotriphosp- hazene;mechanical property;flame-retardant property