Abstract: Oxygen is an important factor affecting the fire hazard and residues trace of combustible materials. In this paper, flame propagation calorimeter, camara, scanning electron microscope and other methods were used to study the combustion performance, residues trace of the flame retardant flexible polyurethane foam （FUPF） and flame retardant medium-density fiberboard （MDF） at different oxygen volume fraction. And the effects of oxygen volume fraction on the related properties of them were analyzed and summarized. The results show that FPUF and MDF were both flame retardant composites, but due to the different materials and flame retardant mechanism, the influence of oxygen volume fraction on the fire risk of them was very different. With the decrease of oxygen concentration, the fire growth index（FGI） of FPUF decreased significantly, while the FGI of MDF also decreased, but the degree of influence was much weaker than that of FPUF. In addition, with the decrease of oxygen volume fraction, the residues amount of FPUF increased, the integrity of the structure was significantly improved and the residues gradually turned black brown. The macroscopic state of MDF earthy-yellow residues was cracked on the macro level. With the decrease of oxygen volume fraction, the cracking crack got wider, with increased black carbonization and enhanced microscopic fibrosis.

Key words: flame retardant composites, oxygen volume fraction, fire hazard, trace characteristics