Abstract: An electrolytic silver catalyst with adding Re and Cs was prepared and used in the reaction of ethylene epoxidation. It has been found that both the activity and selectivity on Ag-Re-Cs are higher than that on Ag. Re can stabilize the catalytic performance of electrolytic silver catalyst with promoter Cs. TDS, WF and TPSR were also used to investigate the adsorption of oxygen and the function of Re and Cs. It can be seen that oxygen adsorbed on the surface has three states: molecular oxygen, atomic oxygen and subsurface oxygen. The adsorbed atomic oxygen is the common oxygen species for both ethylene epoxidation and combustion; molecular oxygen plays no direct role in either two reactions. The role of Re is to suppress the total oxidation of the ethylene, and Cs is to suppress the further oxidation of ethylene oxide. They work in cooperation, which make Ag-Re-Cs catalyst show higher activity and selectivity.