To study the effect of TZM（Mo-0.5Ti-0.1Zr）alloy interlayer on the electron beam welding characteristics of molybdenum-lanthanum-yttrium alloy,the microstructure and mechanical properties of the welded joints were analyzed. The results show that through crack occurred in directly electron beam welding joint of molybdenum lanthanum and yttrium alloy,but the effective welding of molybdenum-lanthanum-yttrium alloy is realized with TZM alloy interlayer. The addition of Zr element reduces the segregation of Mo Oxide at grain boundaries and improves the strength of grain boundary. The microhardness of the joint varies from region to region,the microhardness of the weld zone is equal to that of the base metal,which is 270 ～290 HV,and the HAZ has the lowest microhardness. The mechanical property of the electron beam welded joint of molybdenum-lanthanum-yttrium alloy with TZM alloy interlayer is improved significantly. Fracture occurres in the weld zone during tensile test with a brittle intergranular fracture mode.