The photocatalytic oxygen reduction reaction (ORR), particularly the one-step two-electron (2e⁻) pathway, is a highly promising strategy for efficient and selective hydrogen peroxide (H₂O₂) synthesis. However, constructing efficient photocatalysts to achieve a one-step 2e⁻ ORR process remains a significant challenge. Herein, we developed an efficient photocatalyst by incorporating pyrimidine units into benzotrithiophene-based covalent organic framework (BTT-MD-COF), enabling the photosynthesis of H₂O₂ via the one-step 2e⁻ ORR pathway with O₂ and water. Under visible-light irradiation, BTT-MD-COF exhibited a high H₂O₂ production rate of up to 5691.2 μmol·h⁻¹·g⁻¹. Further experimental results and theoretical studies revealed that the introduction of pyrimidine units accelerates the separation of photoinduced electron–hole pairs and promotes Yeager-type O₂ adsorption, which alters the two-step 2e⁻ ORR process to the direct one-step 2e⁻ process. This work offers a new avenue to create metal-free catalysts for efficient photosynthesis of H₂O₂.