One kind of nano silica was prepared by KH550 and TEOS via sol-gel method, and this kind of nano silica was then applied for modification of solvent free polyurethane used for Paper/Al laminating. The chemical structure and morphology of the nano silica were characterized by FT-IR, SEM and laser particle size analyzer. The mechanical properties of the polyurethane polymer were well studied by Universal tensile testing machine, shore durometer and thermogravimetric analysis. Results indicated that KH550 was successfully synthesized to the nano silica and the particle size of the silica was within sub-micro. The adding of nano silica enhanced the bonding strength of the polyurethane but increased the hardness of the cuing film. Meanwhile too much nano silica with low density was hard to disperse evenly in the film. The content of nano silica should be controlled within 0.8%wt.