A series of copper-silver bimetallic powder was prepared by a chemical replacement method. In this process, ionic masking agent was added to eliminate copper ammonia complex ions adsorption on copper powder surface, which realizes silver continuous coating on the copper powder surfaces. The masking mechanism and the main influencing factors were analyzed. Besides that, TEM, TGA and XRD were used to characterize the Cu-Ag bimetallic powder. Results show that the copper-silver bimetallic powder with the ionic masking agent is of a continuous coating type structure, which has good dispersity, effectively improving antioxidation properties of the copper powder.