22MnB5 hot-formed steel and 6061 aluminum alloy are generally used in the automobile industry. Realizing the connection of these two materials and giving full play to the excellent properties of both materials will no longer only achieve the purpose of lightening the vehicle, but also make certain automobile safety. The low strength of aluminum/steel dissimilar welded joint has been a significant issue restricting their use. The CMT (cold metal transfer) Advanced Pulse (CMT+A+P) welding approach and ER4043 welding wire with a diameter of 1.2 mm were used in this work to achieve effective joining of dissimilar joints in 6061 aluminum alloy and 22MnB5 hot-formed steel with low heat input. The macroscopic morphology, microstructure, and interfacial properties of the fusion brazed joints were analyzed, and the fracture location and fracture morphology were observed by the usage of metallographic microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results showed that when welding heat input increased, the melt width of fusion brazed joint grew steadily and the wetting angle rose initially and fell subsequently. The welding zone was arranged as α-Al equiaxed and Al-Si eutectic, with the Al-Si eutectic equally distributed on the α-Al grain boundary. The grain became coarse because the heat affected zone on the side of the aluminum alloy was subjected to thermal cycling during the welding process. Al and Fe atoms near the interface zone diffuse with each other along the interface layer, and generate various Fe-Al intermetallic compounds. When the heat input increases from 41.8 J/mm to 127.6 J/mm, the thickness of the interface layer grew from 1.49 to 2.85 μm. The fracture appeared at the aluminum alloy base material, the welded joint, and the interface layer, which were ductile fracture, ductile/brittle mixed fracture, and brittle fracture, respectively. The specimen with the highest tensile strength fractured at the aluminum alloy base material, exhibiting ductile fracture, and the tensile and shear loading is 3.88 kN.