Based on the electron gun of SDS-3 electron beam lithography machine, the concave hyperboloid Wehnelt ( oxide-coated cover) of accelerator is discussed. The electron trajectories and potential distribution are given. 以SDS3电子束设备的电子枪为基础,讨论了双曲凹面加速器维纳尔(外敷碱土金属氧化物盖)的电子轨迹与能量分布。