Abstract: Effect of different beam offset on microstructure configuration, thickness of intermetallic compound layers, crack defects and mechanical properties of aluminum alloy/steel electron beam welded joints was analyzed. The results showed that with the increment of beam offset, the Fe-Al intermetallic compound grains in the weld vanished, gradually the eutectic substance on the crystal border decreased, and the configuration of the intermetallic compound layer became less complicated and the thickness of it became smaller. When the beam offset was relatively small, cracks existed in the compound layer; when the beam offset was relatively large, cracks existed in the weld near the compound layer. The optimal tensile strength of the joints was 125 MPa as beam offset 0.5mm. The morphology of the fracture changed with different beam offsets. The optimal thickness range of the compound layer was about 0.9~1.55μm, which was determined by the characteristic of the electron beam.