In this paper, the key problems of catalyst deactivation caused by the formation of green oil on the surface of acetylene selective hydrogenation Pd⁃Ag catalyst were investigated. XRD and H2⁃TPR were used to characterize the composition and the structure of catalyst. The selective hydrogenation performance of Pd⁃Ag catalyst for acetylene and the formation of green oil precursor C4 olefins during the reaction were investigated by using a 10 ml fixed bed high pressure hydrogenation unit. The results show that there are significant differences in the acetylene hydrogenation activity of Pd⁃Ag/Al2O3 catalysts in several different preparation processes, which mainly depend on the dispersion of Pd on the catalyst surface. The close mixing between the promoter Ag and the active center Pd can enhance the electrons and geometric effect, more Pd⁃Ag alloy phase is generated, which reduces the hydrogenation activity of the catalyst, but increases the stability of the catalyst; while the amount of C4 olefins is positively correlated with the activity of the catalyst. The higher the catalyst activity, the more C4 olefins are generated. The conclusion of this study reveals the deactivation mechanism of Pd⁃Ag catalyst, which has important guiding value for catalyst modification and process condition optimization.