Using CO as the probe molecule, infrared diffuse reflectance spectroscopy was used to study the adsorption of Pd⁃Ag/Al2O3 catalysts prepared by impregnation method and the carbon monoxide adsorption on the support and a series of changes in the surface species of the catalyst. The results showed that in the Pd⁃Ag/Al2O3 catalytic system, due to the different order of silver addition, the active center of the catalyst was affected by the electronic effect and the geometric effect, which caused the surface species adsorption morphology of the catalyst after CO adsorption. It was found that there was no bridge adsorption of CO on Pd⁃Ag/Al2O3⁃LM⁃2 catalyst when CO was adsorbed and desorbed before and after heating. The characteristic peak intensity of HCO〖_3^-〗 was found decreased with the increase of CO adsorption and desorption temperature. At the same time, the adsorption characteristic peak of HCOO- was relatively enhanced, and the consistent growth and decline relationship between the two indicated that HCO〖_3^-〗 was converted to HCOO- during the heating process.