A new photoanode RGO/SnO2/TiO2 nanocomposite material with a heterojunction structure was fabricated via hydrothermal method. The RGO/SnO2/TiO2 composite with different graphene content were prepared to explore optimal photoelectrochemical properties compared with pure TiO2. The morphology, structure and optical property of the obtained composite were characterized by TEM, FTIR, XRD and UV-vis. The photocathodic protection effect and anticorrosion properties of the nanocomposite for 304 stainless steel (304SS) were investigated by photocurrent density, open circuit potential, Tafel polarization curves and electrochemical impedance spectroscopy. The results show that compared with pure TiO2, the composite can provide an effective protection for 304SS not only under white light irradiation but also in the dark, and the optimal sample electrode potentials negatively shifted to -590 mV under illumination. The possible photocathodic protection mechanism of the composite was also proposed.