The dissolution mechanism of marmatite in the presence of Cu²⁺ was intensively studied by experiments and density functional theory (DFT) calculations. Leaching experiments showed that Cu²⁺ accelerated marmatite dissolution at high temperatures (above 55 °C), but the trend was reversed at low temperatures (below 45 °C), which may be because the reaction mechanism between Cu²⁺ and marmatite changed from surface adsorption to bulk substitution with increasing temperature. The substitution reaction caused more zinc atoms in the marmatite crystal lattice to be released and enhanced the electrochemical reactivity, while the adsorption of copper ions at low temperatures would passivate marmatite, thus inhibiting the reaction process. DFT calculations showed that the energy of the substitution reaction was more negative than that of the adsorption reaction at high temperatures, which further verified the proposed mechanism.