Electron beam welding experiments of TZM alloy and 30CrMnSiA steel butt joints were carried out with different beam currents.Microstructures and chemical compositions of typical zones were analyzed by optical microscopy,scanning electron microscopy and X-ray diffraction.The mechanical properties of the joints were evaluated by tensile strength tests.Besides,nanoinden-tation tests were carried out to compare the brittleness of the reaction layer and other typical microstructures.The results illustrated that the reaction layer at the interface between fusion zone(FZ) and TZM alloy was the weak position of the joint,which was divided into Fe2Mo layer and a mixture layer of Fe2Mo and α-Fe phases.As the beam current increased,the thickness of the Fe2Mo layer decreased,which resulted in the increasing of the tensile strength of the joints.When the beam current exceeded 24 mA,the formation of the joint was poor with a low tensile strength.When the beam current was 24 mA,the joint presented the highest strength of 191.3 MPa and the joint frac-tured along the Fe2Mo layer near the TZM alloy side with a brittle fracture mode.