Abstract: Aluminum alloy/steel dissimilar metal joining structure has a wide application prospect. CMT welding and pulsed arc welding tests of 6061 aluminum alloy/ DP600 steel dissimilar metals were carried out by using ER4043 welding wire.The welding processes were studied by high-speed camera.The effects of welding modes and process parameters on the microstructure, interface layer and mechanical properties of the lap joints were analyzed. The experimental results show that compared with pulsed arc welding, CMT welding can realize the fusion brazing of aluminum alloy and steel under low heat input, and effectively control the formation of intermetallic compounds, the welding process is stable, the weld forming is good and the welding efficiency is higher. With the increase of heat input of CMT welding and pulsed arc welding, the thickness of the interface layer gradually increases. When the current of CMT welding is 65 A, the heat input is 1.97 kJ/cm, the thickness of interface layer at the steel side is about 3 μm, and the lap joint strength is the highest.