A space electron gun for welding was designed, in which LaB₆ is chosen as cathode material and the cathode is heated by indirect cathode. The initial values of the electron gun are obtained by using the comprehensive iterative method of Vaughan. According to these initial values, the three-pole structure of the electron gun is designed, and then the double magnetic lens is designed. The results show that the parameters of the three electrodes and the lens of the electron gun are adjusted to make the simulation results meet the requirements of the actual design. At the same time, the regularity of the lens debugging process is analyzed. The simulation results show that the design meets the target parameters of 60 mA total emission beam, 0.3 mm cross spot diameter and 0.4 mm beam spot at 300 mm working distance. This design method and the whole design process can provide some reference for the design of electron gun.