Abstract Obtaining a homogeneous distribution of interfacial layer in the Al/steel butt joint could further improve the tensile properties of well-formed joint, which is of great significance to the application of Al-steel hybrid structures in engineering. This article successfully used laser-metal inert-gas (MIG) hybrid welding-brazing technology to obtained 2-mm-thick 6061-T6 aluminum alloy and 301 stainless steel dissimilar metals butt joint. The penetration ability of the hybrid heat source was improved by increasing the laser power within an appropriate range. The interfacial layer with the most uniform thickness (4.5 μm–5.2 μm) and phase composition (τ5 phase and θ phase) could be obtained at laser power of 2000 W. Numerical simulation results revealed that reducing the difference of peak temperature along Al/steel interface could effectively improve the uniformity of the interfacial layer. The smallest difference of interfacial temperatures in the joint produced at laser power of 2000 W was responsible for the most uniform interfacial layer. The tensile strength of the Al/steel butt joint with the most uniform interfacial layer could reach the maximum value of 198 MPa (about 70 % of the 6061-T6 tensile strength).