Tuning the electronic structure is fundamental to improve the optical character and redox ability of photocatalysts. Thus, in this article, g-C₃N₄ with sodium and oxygen co-doping and cyano groups (NOCCN) was successfully synthesized by a brief one-step thermopolymerization. The results indicate that introduction of sodium and oxygen dopant and cyano groups bring a narrower band gap for NOCCN, adjust the overall electronic structure of NOCCN in the positive direction, and facilitate more efficient electron migration ability, which promoted NOCCN achieving photocatalytic water splitting oxygen evolution rate of 1.26 mmolh⁻¹ g ^− 1 without the assistance of any co-catalyst. Furthermore, DFT calculation and related experimental results was also combined to confirm the chemical structure of NOCCN. Obviously, this paper provides a feasible tactic to inflect the electronic construction of g-C₃N₄, improving its oxidizing ability.