Abstract: Arc welding of aluminum was investigated using argon,helium and nitrogen ternary gas,and solid joint with high quality was attained. The experimental results show that with the ternary gas,the arc constricted remarkably,the droplet transferred stably,and the distribution of arc energy density and temperature field was changed during MIG welding of aluminum alloy. In comparison to the MIG welding with pure argon,under the same welding current,the penetration was deeper,the fluid flow in the welding pool and the microstructure of the joint were improved,the impact toughness and fatigue strength of the joint were enhanced. Meanwhile,the cathode cleaning range was narrower, the surface glossiness of the weld was better,and the operation of welding was easier. The experimental results display that the MIG welding with ternary gas could improve the quality of the aluminum weld and is valuable in engineering application.