Abstract: The combined heat source model is used to simulate the distribution of the electron beam welding(EBW) temperature field of Al-Li alloy, based on which, the residual stress distribution of weld zone was calculated through thermo-mechanical coupling. The results show that the temperature field of Al-Li alloy weldment presents an elliptical distribution along the welding direction. The temperature of heat source center is the highest, and the isothermal distribution is dense when adjacent to heat source and gradually becomes sparse with its increasing distance away from the heat source center. There exists a large temperature gradient in weld zone. The nail-shape characteristic of EBW joint is well simulated. The simulation results of residual stress show that the residual stress is mainly generated in the weld zone, and the stress value is higher in the upper part of joint due to the thermal effect by the modification welding. According to the results of numerical simulation, the welding parameters are optimized. The welding experiment demonstrates that the experimental weld morphology is consistent with the simulated molten pool, verifying the reliability of simulation results.