To overcome the high cost and complex preparation of cocatalysts in photocatalytic H₂ production, this study pioneers a triple-benefit strategy in visible-light-absorbing semiconductors through microstructure optimization, electronic property modulation, and active site modification in two-dimensional (2D) hexagonal ZnIn₂S₄ (ZIS) via Sn atom doping. Facilely synthesized through a one-step hydrothermal method without surfactants, 4–6 nm thick Sn-doped ZIS nanosheets exhibit reduced charge recombination by preventing excessive self-assembly and aggregation. Density Functional Theory (DFT) and X-ray Absorption Fine Structure (XAFS) confirm Sn’s substitution for Zn on (001) surface, shifting the Fermi level into the conduction band to facilitate electron migration and charge separation. This adjustment also modulates the electronic properties of adjacent S atoms, triggering the inert basal plane for an enhanced H₂ evolution reaction kinetics. Consequently, Sn-ZIS achieves a H₂ evolution rate of 62.18 μmol h−1 under visible light, significantly outperforming pure ZIS and Pt@ZIS by 6.7 and 3.5 times, respectively.