Photocathodic protection is an economical and environmental metal anticorrosion method. In this research, we successfully synthesized the g-C3N4/GO (15 wt%)/MoS2 catalytic materials by a facile hydrothermal method. The results show that the as-prepared g-C3N4/GO (15 wt%)/MoS2 composites prominently enhanced photocatalytic activities for the photocathodic protection of 304 stainless steel (SS) compared with the corresponding pristine g-C3N4 and MoS2. Notably, the AC impedance results demonstrated that the Rct value of 304 SS coupled with g-C3N4/GO (15 wt%)/MoS2 decreased to 35.66 Ω•cm2, which is 29 and 37 times lower than that of g-C3N4 and MoS2 alone. In addition, g-C3N4/GO (15 wt%)/MoS2 provided the highest current density (77.19 μA•cm2) for the 304 SS, which is four times that of pristine g-C3N4. All results indicate that as-prepared g-C3N4/GO (15 wt%)/MoS2 photocatalysts have produced a distinct enhancement on photocathodic protection performance. An optimum decorating amount of MoS2 onto g-C3N4 forms heterojunctions of g-C3N4/MoS2, which favor the separation of electrons and holes efficiently. Furthermore, the addition of GO further promotes the separation and transfer of photo-induced carriers.