Abstract: Electron beam welding (EBW) with multi-beam method that employs the main beam for welding and two other beams for pre-heating the material regions simultaneously on both sides of the welding seam from a certain distance was proposed for mitigation of welding distortions of thin plates. The uniform rectangular assistant heating source model was established. The numerical simulation of EBW with multi-beam for 1.5 mm thick 304 stainless steel sheet by the thermo-elastoplastic finite element analysis (FEM) method and corresponding experimental test was carried out. The results showed that the simulation values of welding residual stresses and distortions were accordant with the measured values well. EBW with multi-beam can change the stress state of the materials located in front of the molten pool and reduce the peak value of compressive stress of the same position at the moment of molten pool formation, which can effectively reduce the compressive plastic strain, so as to decrease the welding distortion of thin plate.