The CO2 methanation reaction not only addresses energy problems but also fixed atmospheric CO2, thereby mitigating the greenhouse effect. However, as a complex heterogeneous catalytic process, the CO2 methanation reaction requires the synergistic effect of the support and the active metal. As one of the components of catalyst, the promoter significantly influences the physical and chemical properties of the active metal and support. This article reviews the effects of promoters on the structural characteristics of CO2 methanation catalysts, including the dispersion and reducibility of active metals, as well as the oxygen vacancy and basicity of the support. Detailed discussions are provided on strong metal-support interactions, electron transfer, and the H-spillover effect. The addition of a promoter can enhance the catalytic performance of CO2 methanation catalysts, primarily due to their impact on the reaction mechanism. Finally, this article discusses how the promoter improves the catalytic performance by changing the reaction intermediate from a mechanistic perspective.