Cu and other elements in waste acid from copper smelting flue gas sulphuric acid system have high extraction value. In this paper aiming at the precipitation reaction process of Cu2+ with S2O2-3, through experiments, thermodynamic calculation, and product characterization, the precipitation reaction way of Cu2+ was systematically investigated and analyzed. The kinetic parameters of the main reaction and the side reaction in the vulcanization system were determined experimentally to clarify the law of factors which affect the reaction rate. The experimental results show that: S2O2-3 and Cu2+ directly participate in the reaction to produce CuS, and the reaction process is accompanied by the disproportionation side reaction of S2O2-3 and H+. The reaction order of S2O2-3+Cu2+ is higher than that of S2O2-3+H+, and the reaction activation energy of the former is greater than that of the latter. Therefore, increasing the concentration of the vulcanizing agent and increasing the reaction temperature can significantly increase the main reaction selectivity. When the reaction temperature is 80 ℃, the molar ratio of S2O2-3 to Cu2+ is 2∶1, and the reaction time is 120 min, the removal rate of Cu2+ reaches 99.45%.