Abstract: Electron beam welding of pure aluminum to steel with beam deflection was carried out. The microstructure and phase constitution of the joint was examined by optical microscopy,scanning electron microscopy, EDS and XRD. The tensile strength of the joint was also tested. The results show that the alloying process and thermal distribution was improved. The interface between the weld and steel was well bonded with uniform microstructure. The fusion zone on aluminum side was characterized by a transition layer with inner intermetallic compounds. The tensile strength of the joint could be increased with appropriate beam deflection. In this paper, the highest tensile strength was obtained in a joint welded with beam deflection of 0.5 mm to steel side. The joint strength was weakened by the intermetallic compound layer. The fractured surface showed a brittle cleavage fracture mode.