Abstract: The electron beam welding (EBW)of Ti-43Al- 9V-0.3Y(at.%)alloy was carried out with different welding parameters. The effect of heat input on the joint microstructure, formation of weld and tensile strength was investigated.The results showed that the tensile strength increases with the increase of the heat input and decreases with the excessive heat input.The TiAl based alloy was sensitive to the microstructure.The insufficient structural transformation in the EBW joint results in the poor deformability.The transverse macroscopic cracking and longitudinal cratermicrocrack tend to formation.The transformations in the microstructure and hardness in the near weld are severe.This region is weak.Thus the crack propagates from the crater to the near weld and the fracture is a typical brittle properties, which presents cleavage fracture and transcrystalline fracture.Moreover, the layered and cross-measure fracture can be observed.