Abstract: The numerical simulation of vacuum electron beam welding for AZ61 magnesium alloy sheet with 10 mm thickness was studied.By using the finite element model and the 3D moving double ellipsoid heat source model, numerical simulation method was employed to study the influence of the electron beam current on the temperature field of welding process and weld penetration.The results of simulation and experiment show that the effect of deep penetration of electron beam welding can be accessed by the model rebuild.The simulation result of the weld forming and the temperature distributions of weld zone and heat affect zone is more consistent to the experiment result.It also proves that the model is applicable to the finite element simulation on the electron beam welding of AZ61 magnesium alloy sheet.