Abstract: Effects of the mass fraction of nano-SiO₂ on the mechanical properties of the epoxy composite paint film on the steel plate, such as the hardness, the T-bending performance and the strain were investigated in detail. The corrosion resistant properties of the paint films were measured by the salt spray test and EIS (Electrochemical Impedance Spectroscopy). The results indicate that the performances of the composite paint film with 2.0wt% nano-SiO₂ are obviously improved in comparison with the paint film without nano-SiO₂. The hardness of the composite paint film increases from H to 2H, the T-bending improves from 4T to 2T, and the anti-salt spray time improves from 720h to 1030h before showing blisters. The resistance of the composite paint film with 2.0% nano-SiO₂ is two orders higher than that of the paint film without nano-SiO₂ by EIS. Moreover, the nano-SiO₂ particles disperse uniformly in the paint film characterized by SEM images.