Bimetallic catalysts have been widely used for CO methanation because of their superior activity and stability. Herein, Ni-Co bimetallic catalysts supported on SiO2, xNi-yCo/SiO2 (x and y refer to the loading of Ni and Co), are fabricated for CO methanation. For 6Ni-9Co/SiO2, CO conversion is higher than other catalysts with only Ni and Co or both Ni and Co of different ratios. The stability of the 6Ni-9Co/SiO2 is much better in comparison with the 15Ni/SiO2 and 15Co/SiO2. The diffuse reflectance infrared Fourier transform spectroscopy study shows that for both 6Ni9Co/SiO2 and 15Ni/SiO2, CHO is generated first. However, the bimetallic Ni-Co catalyst follows a distinctive reaction pathway subsequently: the C-O bond of CHO breaks first and then CH hydrogenates to form CH4. However, for 15Ni/SiO2, the CHO intermediate first reacts with *H to form CHOH, then C-O breaks, and CH4 is formed. This work well reveals the relationship between the performance of bimetallic catalysts and their reaction mechanism for CO methanation and sheds light on the further development of other bimetallic catalysts for various applications in catalysis.