In order to alleviate the increasingly serious energy problems, the researches and developments of photocatalysts with efficient solar energy utilization, low price and cost, and long-term stability are the critical problem to expand the application technology of photocatalysis. In this work, Co doped Sn3O4 and g-C3N4 were constructed into an S-scheme Co–Sn3O4/g-C3N4 heterojunction photocatalytic system by simple and feasible solvothermal method for photocatalytic H2 evolution. And different loading amounts of Co–Sn3O4/CN-X were obtained by mean of changing the dosage of Co–Sn3O4. The synthesized photocatalysts represented exceptional H2 evolution performance under visible light irradiation (λ>420 nm), among which Co–Sn3O4/g-C3N4-3 showed the best performance, and the H2 yield reached 1793.88 μmol h−1 g−1. This value was significantly higher than that of single catalysts Sn3O4 (294.82 μmol h−1 g−1) and g-C3N4 (1111.28 μmol h−1 g−1). Moreover, the H2 yield of reused Co–Sn3O4/g-C3N4-3 sample kept above 1737.67 μmol h−1 g−1 during cyclic test. XPS, UV–vis DRS and a series of photoelectrochemical analysis ascertained the establishment of internal electric field and bending of the energy band between the interface of Co–Sn3O4 and g-C3N4, which provided the possibility for Co–Sn3O4 and CN to construct Co–Sn3O4/g-C3N4 S-scheme heterostructure. What's more, the mechanism of producing H2 on the surface of Co–Sn3O4/g-C3N4 by oxidizing H2O was proposed. This work demonstrated the application prospect of reasonably designing g-C3N4 based photocatalysts with exceptional stability, sterling functionality and prominent efficiency for H2 evolution, and provided availed guidance for the research and development of g-C3N4 based photocatalysts.