Dissimilar joining of 6 mm thick steel/Al butt joints was carried out using a novel laser offset welding process. The effect of the different locations at the interface on the intermetallic compound (IMC) layers of the joints produced by two different laser powers was investigated. Microstructure inhomogeneity of the IMC layers was investigated in terms of phase morphology, thickness, grain size, main component and phase compositions. As a result, the IMC layer at the interface has the same phase types consisting of η-Fe2Al5 and θ-Fe4Al13 phase for the three locations produced by two laser powers. However, the morphology of the θ-Fe4Al13 phases, the grain size and the thickness of the η-Fe2Al5 layers, and the predominant component in the IMC layers is strongly affected by the laser powers and the locations at the interface. The highest UTS of 85.5 MPa is obtained at the middle location due to the formation of the thinner η-Fe2Al5 layers and the minimum amount of θ-Fe4Al13 phases. Decreasing laser energy inputs effectively improves the IMC layer uniformity, and the influence of locations at the interface on the IMC layer thickness will be weakened with further decreasing the energy inputs. The heating temperature at the interface has a very important impact on the thickness of the η-Fe2Al5 layer attributed to the ferrite or austenite phases appeared in the steel substrate affecting the growth rate of the η-Fe2Al5 layers.