Carbon nitrides (g-C3N4) is considered to be the prospective semiconductor photocatalyst for photocatalytic H2 evolution. Nevertheless, it suffers from low charge transfer efficiency and fewer metal active sites. Thereby, Ni-Sn3O4/g-C3N4 photocatalysts were constructed by anchoring Ni-doped Sn3O4 microflowers on g-C3N4 via a feasible and straightforward solvothermal treatment. The prepared Ni-Sn3O4/g- C3N4 S-scheme heterojunction could improve the transfer and separation efficiency of photo-generated electron-hole pairs by facilitating the electrons transfer from Ni-Sn3O4 to g-C3N4. Moreover, the photocatalytic H2 production performance was ameliorated due to the established internal electric field and the energy band bending in Ni-Sn3O4/g-C3N4 S-scheme heterojunction. Meanwhile, the doping Ni in Sn3O4 exposed more active sites in Ni-Sn3O4/g-C3N4 heterojunction for producing H2. As a result, Ni-Sn3O4/g- C3N4-5 photocatalyst exhibited outstanding H2 yields of 1961 µmol h-1 g-1 under visible light irradiation in comparison with pure Ni-Sn3O4 (12 µmol h-1 g-1) and bared g-C3N4 (1391 µmol h-1 g-1). Furthermore, the S-scheme mechanism in Ni-Sn3O4/g-C3N4 heterojunction for producing H2 by oxidizing H2O was proposed. This study provides helpful guide for developing efficient g-C3N4-based photocatalytic systems.