Abstract: According to the performance requirement of the electron gun to be worked in the space environment, the optical system of 10 kV space electron gun is designed, along with simulation analysis. Firstly, the trajectory of the electron beam is obtained through the simulation with the proper cathode material. Then, the appropriate focal length is determined and a single-lens focusing system is simulated. In view of the restriction of the capability of the single-lens focusing system, a two-lens focusing system is designed to meet the requirements. A complete set of design methods and processes is given in this paper. The simulation results show that by the above methods, the electro-optical parameters can be optiized to meet the engineering requirements. This research can help the future design of space electron guns.