Abstract: The electron beam welding experiment is carried out on 10 mm thick CuNi90/10 plate. The small surface tension of the liquid metal results in the narrow welding process window, therefore, the large heat input would lead to the weld face concave. The effect of one-side welding with back formation for the CuNi90/10 alloy is not as good as that of the titanium alloy. The optimized parameters can obtain the weld face slightly concave and overall good back side appearance. RT and PT results of the weld with GTAW covering can meet grade I standard of NB/T 47013-2015, and the mechanical properties can meet the requirements of NB/T 47014-2011. The columnar crystal feature in the weld zone is obvious, the impact performance is good, with the impact energy reaching 200 J, and the hardness of the weld zone decreases compared with that of the base metal. The appearance of EB weld zone is characterized by large depth to width ratio. The microstructure of weld zone is dendrite α and that of the heat affected zone is twin α. The nickel-rich α phase is bright and the copper-rich α phase is dark under the optical microscope.