Abstract: Typical refractory metals, including molybdenum, tungsten, tantalum, and niobium, are critical materials in aerospace, nuclear energy, and high-end electronics. Their high ductile-to-brittle transition temperature, severe grain coarsening tendency induced by high thermal conductivity, and extreme sensitivity to interstitial impurities pose significant challenges to fusion welding. Electron beam welding, with its high-vacuum environment and precise heat input control, has become a core technology for achieving high-quality joints. This paper systematically reviews the process characteristics, weld microstructure, mechanical properties, and formation mechanisms and control strategies of typical defects in electron beam welding of these four refractory metal systems. The analysis indicates that for molybdenum and its alloys, the key is to overcome grain boundary embrittlement and porosity; for tungsten and its alloys, the core bottleneck is cracking susceptibility; tantalum and its alloys exhibit good weldability for similar joints, but dissimilar connections are dominated by brittle intermetallic reaction layers; niobium and its alloys can achieve equal-strength matching for similar joints, while the performance of dissimilar joints is still constrained by Laves phases. Finally, future directions for enhancing joint reliability through multi-physics simulation, intelligent monitoring, and novel interlayer design are proposed.