Polypropylene(PP)/nano-SiO2 composites were prepared through direct melt mix processing method. The results showed that silane coupling agent had certain effect on the dispersion of nano-SiO2, and the nano-SiO2 particles were well-distributed in PP matrix when mixed PP-g-MAH acted as compatibilizer. The properties of PP/SiO2 were optimum at 2 % nano-SiO2, compared with pure PP, the Izod impact strength increased 90 %, the tensile strength increased 5 % and the flexural modulus increased 23 %. Finally, the mechanism was deduced on the reason why PP-g-MAH could improve the dispersing effect of nano-SiO2 particles in PP matrix.