Abstract: In order to investigate the mechanical properties of commercial plastic polypropylene (PP) reinforced with inorganic rigid particles, the PP composite material filled with the surface-modified silica particles by silane coupling agent A-151 was prepared by the melt blending method. The effects of the particle size, mass fraction of silica, surface modification of silica and mixture of the silica particles with different sizes on the toughening and strengthening of PP matrix were investigated based on the results of mechanical properties testing and the observation of the impact fracture surface morphology of the composites. The results show that the toughness, strength and rigidity of the composites can be improved simultaneously by filling nano silica particles into polypropylene. The finer the size of the particles is, the higher the mechanical properties of the composites are. When the modified silica particles are filled into PP, the dispersion of the silica in PP matrix and the compatibility between the silica and matrix are improved, and the mechanical properties of the composites are improved. The composites reinforced with the mixture of the silica particles with different sizes have higher tensile and flexural properties. The mixture has a better reinforcing effect on PP matrix, but the impact property of the composites decreases.