AbstractPhotocatalytic oxygen reduction reaction (ORR) is an environmentally friendly and cost‐effective approach for H2O2 synthesis. However, the current photosynthesis system suffers from sluggish kinetics, rapid recombination of photoexcited charge carriers, and weak redox potentials, resulting in unsatisfactory solar‐to‐chemical conversion efficiency. Herein, a Z‐scheme heterojunction (UiO/IKCN) is constructed through coupling I−/K+ co‐doped g‐C3N4 (IKCN) with NH2‐UiO‐66, a typical metal‐organic framework material. Under visible light irradiation, the optimal UiO/IKCN exhibits exceptional H2O2 production rates in pure water (13.3 mM g−1 h−1) and in isopropanol solution (72.6 mM g−1 h−1), that is 48.4 times higher than pristine CN in isopropanol (1.5 mM g−1 h−1). A high apparent quantum yield of 10.28% at 420 nm is achieved by UiO/IKCN, surpassing most previously reported values. The dominating role of two‐electron ORR in H2O2 photosynthesis is elucidated in detail. The significantly enhanced photocatalytic activity can be attributed to the facilitated charge separation and Z‐scheme charge transfer, which are unambiguously verified by stable‐state surface photovoltage, transient photoluminescence, femtosecond transient absorption spectroscopy, in‐situ irradiated X‐ray photoelectron spectroscopy, and density functional theory calculations. This study represents the first exploration of H2O2 production using NH2‐UiO‐66 and provides insights into the rational design of Z‐scheme heterojunction for highly efficient photosynthesis.