CO₂ methanation is of great significance to CO₂ utilization. However, it is challenging to prepare Ni-based catalysts with superior low-temperature activity via a simple method. In this work, a highly active Ni/CeO₂/SiO₂ catalyst is developed by a combustion-impregnation method, and the synergistic effect of active sites for H₂ and CO₂ activation are studied. The research results show that highly dispersed Ni particles (6 nm) are obtained by this method with an instantaneous reaction. As a result of the increased number of Ni active sites, the catalyst exhibits improved catalytic activity. Moreover, addition of CeO₂ promoter further improves the low-temperature activity. First, it enhances the catalyst reducibility, creating more Ni active sites for H₂ dissociation. Second, the surface oxygen vacancies formed on CeO₂ facilitate CO₂ activation. Therefore, the best performance of 63% CO₂ conversion and 99% CH₄ selectivity at 250 °C is achieved on the Ni-5Cesingle bond catalyst with small Ni particles and optimal amount of CeO₂ promoter. With higher CeO₂ content, Ni-7.5Ce catalyst displays decreased catalyst reducibility and catalytic activity. Therefore, it can be concluded that a proper ratio between both types of sites is crucial for CO₂ methanation.