Ca²⁺ and Mg²⁺ are the most dominating unavoidable ions in the smithsonite flotation. In this paper, the effect of Ca²⁺ (Mg²⁺) on the surface of smithsonite sulfidization in a system where water molecules are present was investigated using density functional based tight binding (DFTB+) simulations for the first time. The results indicated that the adsorption of hydrated Ca²⁺ complexes is stronger than that of hydrated Mg²⁺ complexes on the hydrated smithsonite (101) surface. In addition, at low concentrations of sodium sulfide, there is no adsorption of HS- on the surface pre-adsorbed with hydrated Ca²⁺ complexes, but only on the surface pre-adsorbed with hydrated Mg²⁺ complexes. At high concentrations of Na₂S, S^2- weakens the adsorption of hydrated Ca²⁺ complexes due to competitive adsorption, but the presence of S^2- could desorb hydrated Mg²⁺ complexes from the surface. The results compared the differences in effects of Ca²⁺ and Mg²⁺ on smithsonite sulfidization, which could provide an atomic scale basis for researching the surface sulfidization of oxide minerals.