Abstract: The main structure of subway vehicles widely uses high-strength aluminum alloy, which has the characteristics of high thermal conductivity and easy formation of oxide film on the surface. This can easily lead to defects such as incomplete fusion and porosity during the welding process, reducing the application effect of the material. In order to optimize the tensile performance and fatigue resistance of welding joints in subway rail vehicle manufacturing materials, and improve the joint microstructure and properties, the laser MIG composite bottom welding process and joint microstructure and properties of subway rail vehicles were studied. Using A6N01S-T5 aluminum alloy commonly used in subway rail vehicles as the base material and ER5356 as the filler wire, a single-sided V-shaped groove was designed. Laser MIG composite bottom welding tests were conducted on four different welding parameter specimens, M1, M2, M3, and M4, to test the macroscopic forming, internal defects, hardness, tensile and fatigue properties of the welded joints of each specimen. The results showed that among the four groups of specimens, the M4 specimen with a heat input of 2.1 kJ · cm-1 had a uniform and smooth macroscopic forming of the welded joint, and there was only one small pore with a diameter of 0.3mm inside the weld seam; The hardness of the heat affected zone is high, forming a structure with good strengthening effect; The tensile strength reaches 198.25MPa, and the tensile fracture toughness is rich and uniform; At various stress levels, the average fatigue life of M4 specimen welded joints is the highest among all groups. Therefore, when using M4 process parameters with laser power of 5.8 kW, welding current of 320 A, welding voltage of 28.3V, welding speed of 4.2 m/min, and heat input of 2.1 kJ/cm^-1 for welding, the microstructure and properties of aluminum alloy welded joints in subway rail vehicles can be effectively improved.