Electron beam welding was carried out on TC4/TC17 dissimilar titanium alloy, and tensile tests were carried out at 400℃. The results show that there were significant changes in heat-affected zone and weld microstructure compared with base material with the action of welding thermal cycle. The microstructure of heat-affected zone on TC4 side was martensite. The heat-affected zone of TC17 side was metastable β phase, and coarse columnar crystals were observed at the weld. The hardness of TC17 base material was higher than that of TC4 where the hardness of weld center was the highest. The tensile strength of TC17 base metal was the best at 400℃，meanwhile the tensile strength of welded joint was similar to that of TC4 base metal. The fracture surface of TC4/TCI7 electron beam welded joint was characterised by large size, few and shallow tough nests, which were oval in shape and showed good plasticity.