The waterborne acrylic resin modified by both itaconic acid (IA) and γ-methacryloxypropyl triisopropoxidesilane (KH571) was successfully synthesized by the seeded emulsion polymerization. The effects of IA and KH571 on the properties of waterborne acrylic resin, including mechanical properties, water resistance, thermal stability, storage stability and corrosion resistance, were studied. Fourier transform infrared spectroscopy analysis showed that IA and KH571 were successfully copolymerized with acrylic monomers. Compared with the unmodified resin, the introduction of IA and KH571 greatly improved the water resistance of the resin coating. When 2 wt.% IA and 4 wt.% KH571 were added, the contact angle of the resin coating increased from 78.91° to 90.49°. The water resistance time of the resin coating was improved from one day to 17 days. Additionally, the modified resin showed better mechanical properties, thermal stability, storage stability and corrosion resistance. The waterborne acrylic resin modified with IA and KH571 has a potential application prospect in the fields of waterproof and anticorrosive coating.