The work aims to study the impact of nano-alumina (Al2O3) on the mechanical properties and combustion performance of PP/MHSH/Al2O3/N-P composites. First, MHSH and Al2O3 were subject to surface modification treatment. Second, PP, MHSH, Al2O3 and N-P were mixed together by a mixer. Finally, PP/MHSH/Al2O3/N-P composites were prepared by melt blending. When the mass fraction of Al2O3 added was 8%, the mechanical properties of the composites were better, but the mechanical properties of the composites decreased gradually with the increase of Al2O3 content. When the mass fraction of Al2O3 was 5%, the limiting oxygen index (LOI) of the composites was 23.6%, and the flame-retardant properties were obviously improved, but the LOI growth rate of composite system was slowing down with the continuous increase of Al2O3 filling content. The mechanics and comprehensive flame-retardant performance of the composites were the best when the mass fraction of Al2O3 was 8%. In conclusion, Al2O3 is dispersed well in PP base material after the surface modification treatment, and the treatment also works to reinforce and toughen the PP composites, and also improve their flame retardant properties.