A series of MnOx-promoted Ni catalysts supported on Si waste contact mass (W) modified by Al2O3 were successfully prepared by the deposition-precipitation method for CO methanation. Compared with the Ni catalysts directly supported on W, Ni/Al2O3-Si and MnOx-promoted Ni-MnOx/Al2O3-Si catalysts exhibited much better catalytic performance for CO methanation, particularly the latter, which exhibited the least decrease in CO conversion (1%) and lowest carbon deposit (0.3 wt %) in a 110 h lifetime test. The structural characterizations showed the highest Ni dispersion and highest oxygen vacancy concentration in the Ni-MnOx/Al2O3-Si catalyst. The added Al2O3 improves the dispersion of Ni, and the MnOx promoter can restrain the sintering and aggregation of Ni particles during the process of reduction and reaction at high temperatures and provides more oxygen vacancies, which is conducive to the removal of carbonaceous species on the :catalyst surface for anticoking.