Ultrafine nanoparticle or single-atom deposition can improve the photocatalytic activity of graphitic carbon nitride (g-C3N4) efficiently. Herein, we prepared sodium ion-doped g-C3N4 photocatalyst deposited with ultrafine silver nanoparticles ( < 1 nm) by a facile and efficient one-pot route. Sodium sulfate was used as an inexpensive and green precursor to achieve the doping of sodium ions to g-C3N4. Ultrafine silver nanoparticles were anchored in-situ on the surface of g-C3N4 to construct Schottky heterojunction during thermal poly-condensation. The band gap and valence band position of g-C3N4 were tuned by sodium ion doping, which enhanced visible light absorption and oxidizing ability. Both ultrafine silver nanoparticles and sodium ions accelerated the migration of photogenerated electrons and promoted the separation of photogenerated carries. These merits were synergistic to cause the excellent enhanced photocatalytic activity of sodium ion-doped g-C3N4 deposited with ultrafine silver nanoparticles in degradation of Rhodamine B and tetracycline hydrochloride under visible light irradiation.