Abstract: The methanation of synthesis gas is the key process of coal to natural gas. Considering the existence of CO₂ in the synthesis gas, it is important to investigate the influence of CO₂ on the sulfur-resistant methanation. In this paper, the effect of CO₂ on methanation activity of Mo-based catalysts was investigated at the reaction temperature of 550℃ and the gas space velocity of 5000h^-1 with the syngas containing 1.2% H₂S (volume ratio). The results show that the promoter Co and the cerium-aluminum composite support can improve the stability of the catalyst and reduce the deactivation. The CO₂ is proved to promote the reverse water gas shift reaction, which would inhibit the activity of MoO₃/Al₂O₃ catalyst more heavily than MoO₃-CoO/CeO₂-Al₂O₃ catalyst. When the CO₂ adding to the inlet gas is less than 10% for 20h, the catalyst activity could be restored to its original activity after stopping the addition of CO₂. However, as the added CO₂ in inlet gas is over 10%, more H₂O will be generated through reverse water gas shift reaction to damage the catalyst structure and decrease the active component, resulting in an irreversible loss of catalyst activity.