The deactivation mechanism of the simultaneous removal of COS and CS ₂ over a Fe–Cu– Ni/MCSAC catalyst was investigated using SEM/EDS, XPS and in situ DRIFTS methods. The results show that the catalytic hydrolysis of COS and CS ₂ over the Fe–Cu–Ni/MCSAC catalyst involves two steps: hydrolysis of COS/CS ₂ and oxidation of H ₂S. The SEM/EDS and XPS results indicate that that catalytic hydrolysis of CS ₂ can be achieved by the actions of alkaline groups and active components. When O ₂ was introduced into the system, oxidation of H ₂S occurred via H ₂S → S → SO ²⁻ ₄ /sulphate. In situ DRIFTS experiments indicated that the formation of sulphate may occur as follows: (a) H ₂S + O ₂ → S + H ₂O, (b) S+O ₂ → S–O, (c) – COO+H ₂S →–CH+S–O, (d) C–OH+H ₂S →–CH+S–O. The in situ DRIFTS experiments also indicated that the C–OH groups, –COO groups and O ₂ played important roles in the deactivation of the catalyst, which was consistent with the XPS results. Meanwhile, the SO ²⁻ ₄ /sulphate content increased during the reaction, which led to its occupancy of the catalyst’s surface activity sites. Additionally, the alkaline groups and active components were removed, which could also result in the deactivation of the catalysts.