<p>Heavy metal pollution is a globally environmental crisis as the demand for electronic products being steadily on the increase. In our work, a novel transition metal Sn-doping strategy has been proposed to reconstruct the valence band of CdS by s-p orbit hybridization. An easy and mild solvothermal method was employed to synthesize the Sn-doped CdS nanoparticles, in which Sn²⁺ ions substitute Cd²⁺ ions to occupy CdS lattice. This Sn-doping modification effectively narrows the bandgap and regulates the energy band structure of CdS. In this case, it has caused an extension of the visible light absorption range, an enhancement of photogenerated carrier separation efficiency, and an improvement of thermodynamic potential, as well as a photostability from photocorrosion. For the optimization effect of Sn doping, the 4 at% Sn-doped CdS sample has performed the highest efficiency of photocatalytic reduction Cr (VI) degradation, achieving 84.8% Cr (VI) removal within 10&#xa0;min, as 1.3 times higher than that of bare CdS. This research establishes an experimental framework for the advancement of efficient and stable nano-photocatalysts, with implications for band engineering in metal dichalcogenide semiconductors.</p>