Solar photocatalytic water splitting for H2 production, with a simple and cost-effective reaction system, holds significantpromise for addressing the current energy and environmental crises while achieving the “dual carbon” goals. However,traditionalstudies have primarily centered on the design of photocatalytic materials,lacking a systematic and cross-scale understanding of the energyand mass transfer and conversion processes at the reaction interface (involving gas, liquid, and solid phases). This oversight hasresulted in low solar-to-H2 efficiency. This review elucidates the basic principle and processes of photocatalytic water splitting from theperspective of energy and mass flow,and delves into the bottlenecks,including non-steady-state light absorption and energy conversion,slow mass transfer processes (especially the nucleation,growth,and detachment of reaction interface bubbles,and the scarcity of water resources in extreme regions. In response to these challenges, this review elaborates on several breakthrough approaches. Firstly, itintroduces a solar concentrating-photothermal coupling reaction system,which significantly enhances the wide-spectrum utilization ofsolar energy and the reaction potential and conversion efficiency of photogenerated carriers by utilizing concentrated photothermaltechnology to synergize light and heat. Secondly,this review elaborates on the theoretical and methodological foundations for constructinga new liquid-solid/gas-solid decoupled reaction system based on photothermal substrate, effectively overcoming the mass transferlimitations caused by bubble formation in traditional three-phase systems. Thirdly,it discusses the strategy for hydrogen production bycoupling with atmospheric water harvesting and photocatalytic water splitting to address water scarcity issues,utilizing solar frequency-division technology and gas-solid interface construction. Finally,from an engineering perspective,it emphasizes the significant impact andimportance of system design and large-scale demonstration,and proposes future research directions in this field.