Abstract: In order to have great electron flux for scrubbing Φ30nm microchannel plate and complete the process in less time，the trace of electron was analyzed and the electron deflection was calculated, according to the operation principle of the axial electron gun and the theory of the function of electrostatic field on electron. Based on the calculation result, the structure of the new electron gun was designed and all the parameters of the electron gun were determined, the filament material was Φ0.05mm tungsten rhenium alloy（75%, 25%）, the filament was in “∨” type, the radius of the electron gun was Φ35mm and its height was 20mm, and the current density of electron emission reached 1.26×10-5A/cm2 while the maximum filament heating power was 12.6W. The gain of the four microchannel plates reached 500±50 after being scrubbed with the electron gun for four hours. The result indicates that the old electron gun RUSA can be replaced by the new one with better performance.