Flame Retarded PPO/HIPS Resin and PPO/HIPS/ nanometer silicon dioxide(SiO2) nanocomposites were prepared by using aromatic condensation phosphate ester retardant such as resorcinol bis(diphenyl phosphate)(RDP) and bisphenol A bis(diphenyl phosphate)(BDP),nanometer silicon dioxide(n-SiO2),melamine cyanurate(MCA) as additive flame retardant.Discussed flame retarded PPO/HIPS resin's retardant and retardant mechanism by the combination measures of LOI,UL 94,TGA,CONE parameters.Experimental results showed that these systems gained good effect,and RDP was better than BDP if their addition were same.Limiting oxygen index and UL94V flame retardancy of PPO/HIPS reached 35.0% and V-0 grade.