This work aimed to study the burning behavior of polypropylene composites and the effect of nano-SiO2 content on the mechanical properties of the composite. By means of melt blending method, polypropylene, nitrogen and phosphorus compound flame retardant and surface modified nano-SiO2 composite materials were mixed to prepare polypropylene composites. The results showed that: in the process of combustion, nano-SiO2 had some effects on the flame retardancy, and the nitrogen and phosphorus compound flame retardant was a key factor affecting the flame retardancy of the composites. With increasing nano-SiO2 content, the limiting oxygen index of the composites first increased and then decreased. When the nano-SiO2 content was 1% , the limiting oxygen index of the composites was the maximum. With increasing Nano-SiO2 content, the tensile, impact and bending strength as well as the flexural modulus first increased and then decreased. There was a certain synergistic flame retarding effect of nitrogen and phosphorus compound flame retardant and nano-SiO2 on the composite materials. When the nano-SiO2 content was 1% , the composites with optimal flame retardancy and mechanical properties were obtained.