To improve the catalytic activity of CO2 methanation at low temperature, a series of Ni/ZrO2 catalysts with different Ni loadings were prepared by citrate complexing method. Based on the optimal Ni loading of 6 wt%, a certain amount of MgO was doped to improve the thermal stability of Ni/ZrO2 catalyst. When Ni/Mg molar ratio was 4, there was the best performance, getting as high as 90% CO2 conversion and nearly 100% CH4 selectivity at 250 degrees C, 0.1 MPa and a WHSV of 15,000 ml g(-1)h(-1), and the equilibrium CO2 conversion was obtained at 300 degrees C. XRD, BET, TPR, CO2-TPD, H-2-TPD, XPS, TG and TEM were conducted to investigate the reason of high activity of Ni/ZrO2 catalyst at low temperature and the effect of doping MgO. Results suggested that highly dispersed Ni nanoparticles are responsible for the excellent catalytic activity. MgO can effectively improve stability of Ni-based catalysts by the confinement effect. Meanwhile, it is also found that there are little improvements on catalytic activity after doping MgO, and the TOF of catalysts with different MgO doping is basically the same, indicating CO2 can be efficiently adsorbed and activated on the monoclinic ZrO2, and MgO do not contribute to the intrinsic activity.