Abstract: The high soluble carbonate minerals calcite and dolomite associated with the smithsonite will lead to amounts of calcium (magnesium) ions in the pulp, which will affect the flotation of smithsonite. In this work, Density Functional Theory calculations are conducted to investigate the adsorption of calcium (magnesium) ions on smithsonite (101) surface. The calculation results indicate that calcium ions and magnesium ions have strong chemisorption with the surface of clean smithsonite (101), and the adsorption of calcium ions is stronger than magnesium ions. The hydrated smithsonite (101) surface also adsorbed calcium and magnesium ions, but the adsorption intensity was obviously weakened. In addition, the adsorption of calcium ions on hydrated smithsonite surface (101) weakens the hydration of smithsonite (101). The results can provide theoretical guidance for eliminating the influence of unavoidable ions in the flotation process of smithsonite.