Sulfuric acid (H2SO4) is a specific depressor for apatite rather than for dolomite. The H2SO4- treated dolomite can still be floated effectively by oleate. However, the role of H2SO4 in the adsorption of oleate onto dolomite surface remains unclear. In this work, density functional theory calculations were conducted to probe the interactions among sulfate anion (SO42−), oleate anion and the dolomite surface. The adsorption behaviors of SO42− anion onto the perfect and CO3-defect dolomite surfaces were compared. Such results show that SO42− anion could only adsorb onto the defective dolomite surface, where it bonded with a Ca atom. The remaining Ca and Mg atoms at the defect site could further react with the oleate anion, generating new Ca/Mg–O ionic bond. In this regard, oleate and SO42− anions may both present on the dolomite surface. This phenomenon accounts for the flotation of H2SO4-treated dolomite.