The exothermic characteristic of the water-gas-shift (WGS) reaction, coupled with the thermodynamic constraints at elevated temperatures, has spurred a research inclination towards conducting the WGS reaction at reduced temperatures. Nonetheless, the challenge of achieving efficient mass transfer between gaseous CO and liquid H₂O at the photocatalytic interface under mild reaction conditions hinders the advancement of the photocatalytic WGS reaction. In this study, we introduce a gas–liquid–solid triphase photocatalytic WGS reaction system. This system facilitates swift transportation of gaseous CO to the photocatalyst's surface while ensuring a consistent water supply. Among various metal-loaded TiO₂ photocatalysts, Rh/TiO₂ nanoparticles positioned at the triphase interface demonstrated an impressive H₂ production rate of 27.60 mmol g⁻¹ h⁻¹. This rate is roughly 2 and 10 times greater than that observed in the liquid–solid and gas–solid diphase systems. Additionally, finite element simulations indicate that the concentrations of CO and H₂O at the gas–liquid–solid interface remain stable. This suggests that the triphase interface establishes a conducive microenvironment with sufficient CO and H₂O supply to the surface of photocatalysts. These insights offer a foundational approach to enhance the interfacial mass transfer of gaseous CO and liquid H₂O, thereby optimizing the photocatalytic WGS reaction's efficiency.