Synergistic nitrogen reduction and water oxidation process is significant to the photocatalytic fixation of nitrogen. However, the coupling mechanism remains ambiguous and lacks study. Herein, we report enhanced photocatalytic nitrogen fixation on single-atom Fe-modified macro-/mesoporous TiO₂-SiO₂ (Fe-T-S), with a high ammonia generation rate of 32 μmol g^–1 h^–1 without any sacrificial agent and cocatalysts. Experimental and theoretic calculation studies confirmed the formation of a photoinduced hole-trapping polaron on the Fe dopant, resulting in the high-valent Fe(IV) species. The single-atom Fe(IV) site is responsible for water oxidation and helps promote N₂ hydrogenation on neighboring oxygen vacancy. This study explicitly unravels the key to achieve the coupling between photocatalytic N₂ hydrogenation and water oxidation through a doping strategy and provides significant guidance for the rational design of photocatalysts for ammonia synthesis.