Abstract: Welding test for large cross-section cast aluminum and cast steel (dissimilar metals) by continuous drive friction welding technology was conducted. By means of electron microprobe, transmission electron microscopy, X-ray diffraction analysis and micro-hardness testing, the welded joints between cast aluminum and steel were analysed. The results show that the joints between the large cross-section cast aluminum and steel has a good friction weld ability, the main elements diffuse to the dual surface from the interface which is as the starting point, diffusion distance of iron atoms is slightly less than that of aluminum atoms, carbon is induced by secondary friction face to form carbide, not only crystal but also amorphous exist in the weld zone, and the hardness on both sides of weld joint zone is slightly higher than that of the substrate.