In order to reutilize these industrial wastes of pyrite tailings, the effects of the six single factors of sulfuric acid concentration, leaching time, ore particle size, ore dosage, leaching temperature and agitation speed on leaching copper in the pyrite tailings and the subsequent L18(37) orthogonal optimization experiments had comprehensively been investigated. Furthermore, the mechanism inhibiting further acid leaching reaction had been revealed by the scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The research result showed that the optimal condition of leaching copper was sulfuric acid mass fraction of 30%, leaching time of 6 h, ore particle size of 150 ?m, ore dosage of 5 g, leaching temperature of 108℃, and agitation speed of 440 r/min. Under the condition, the Cu leaching rate can reach 50.68%. The priority of influencing factors of sulfuric acid mass fraction>leaching temperature>ore dosage>leaching time>ore particle size>agitation speed was obtained via the range analysis of the orthogonal test, and moreover the six factors were extremely significant via the variance test. Finally, the SEM and EDS had revealed that the surfaces of the leached residues had tightly been encapsulated by micron-sized particulate SiO2, so that it passivated the further leaching reaction progress and limited the constant increase of the leaching rate at the late stage of acid leaching. Therefore, it was very necessary to loosen the SiO2 coating layer and release its passivation at the later stage of leaching reaction for the sake of further improving the leaching copper in the silicon-rich pyrite tailings.