In this work, the significant electron tunneling over iodine-decorated graphitic carbon nitride (I-g-C₃N₄) was achieved by I₃⁻ and I₅⁻ clusters implanted. The flip-flop electron tunneling takes place via strong Rashba spin-orbit coupling in p orbitals of polyiodides. The electron tunneling and hopping bridged the easier transfer route between far-located carbon atoms of g-C₃N₄ through the polyiodides p orbitals. By taking the advantage of this tunneling, the conductivity of I-g-C₃N₄/Ag photocatalyst was remarkably increased and the lifetime of photogenerated charges was largely prolonged, evidenced by I–V characteristics and the photoluminescence (PL) spectra. With the help of these properties, the obtained I-g-C₃N₄/Ag photocatalyst presented high active for hydrogen generation under visible light irradiation and Ag NPs as active site for hydrogen formation. 104.3 μmol H₂ was evolved over I-g-C₃N₄/Ag photocatalyst in 3 h, about three time higher than that of un-iodinated g-C₃N₄/Ag, and no remarkable decay of activity was observed in 900 min reaction. The highest AQE value of 7.3% was achieved at 520 nm.