Density functional theory (DFT) calculations and catalyst performance evaluations were conducted to investigate the promoting effect of H2S on the dehydrogenation performance of the PtSnK/Al2O3 catalyst. The results show that adding an appropriate amount of H2S to the feed gas significantly increases propylene selectivity, which remains above 93%, while improving catalyst stability and reducing carbon deposition. The optimal H2S volume fraction in the feed is 2.4×10⁻5, at which both propane conversion and propylene selectivity reach their maximum values. Excessive H2S, however, causes catalyst poisoning and a substantial decrease in activity. According to the DFT calculation results, among different adsorption configurations, the Gibbs free energy is minimal when H2S and propylene are co⁃adsorbed on both Pt(111) and Pt(211) crystal surfaces. Specifically, the Gibbs free energy on the Pt(211) crystal surface is -0.09 eV, which is lower than that on the Pt(111) crystal surface, which is -0.05 eV. These results suggest that H2S facilitates propylene desorption and preferentially adsorbs on the Pt(211) surface, thereby suppressing side reactions, increasing propylene selectivity, and promoting the dehydrogenation performance of the PtSnK/Al2O3 catalyst.