Abstract: In recent years, the demand for reliable dissimilar metal joining techniques has attracted extensive attention in high-performance fields including aerospace, nuclear reactors and medical devices. Tantalum（Ta） and tungsten （W） are representative dissimilar metals with outstanding merits such as high melting points, excellent corrosion resistance and superior mechanical strength. Nevertheless, the significant discrepancies in their thermal and mechanical properties bring severe challenges to their joining, easily inducing various weld defects. In this work, electron beam welding （EBW） was adopted to explore the effect of beam offset position on the quality of Ta-W alloy joints. The process parameters were optimized, and the welds were systematically characterized by laser confocal microscopy, scanning electron microscopy （SEM） and energy-dispersive spectroscopy （EDS）.The results demonstrate that a beam offset of 0.12 mm toward the tungsten side generates a diffuse fusion line and uniform elemental transition, achieving the optimal joint quality with a forming coefficient of 3.67 and effectively eliminating crater depression and porosity. In contrast, zero beam offset causes obvious weld defects, while offsetting toward the tantalum side leads to serious surface depressions and intergranular cracks.The optimized welding parameters are determined as follows: accelerating voltage of 60 kV, beam current of 8 mA, focusing current of 1 816 mA, welding speed of 900 mm/min, and 0.12 mm beam offset toward tungsten. These parameters realize the sound joining of Ta-W dissimilar metals, which provides a solid basis for engineering applications. This study enriches the understanding of EBW of dissimilar metals and offers effective guidance for the joining of refractory metal combinations.