In LaB6 electron gun,Kramers-Heisenberg scattering and Fermi distribution are analyzed.Based on the electron gun of SDS-3 electron beam lithography machine,when the accelerating voltage is 30 kV,the requirements that the electron trajectories and potential distribution must be realized for concave hyperboloid Wehnelt(oxide-coated cover) of accelerator are discussed.Electrons from the gun will be accelerated by a high voltage and reach a target of silicon piece(Front the aperture) via the Wehnelt.Finally,a new method to measure the resolution of LaB6 electron gun is reported.The measurement results are basically the same theoretical calculation.