Abstract: The Girth welding experiment of 5A06 aluminum alloy with thickness of 6.5 mm was carried out by filler wire and without substrate TIG welding process. Through the optimization of welding parameters, the appearance of weld was well,meanwhile, the microstructure, mechanical properties and microhardness analysis of the welding joint under different welding parameters were analyzed. The results show that the base metal is the original rolled structure,the welding joint is the dendrite structure of the β distributed on the solid α-Al solution grain boundary. The average yield strength, tensile strength and elongation of the welding joint is 151.11 MPa, 374.59 MPa, 18.28%, which is 82.3%,98.7% and 63.6% of the base metal.Compared with the microstructure, mechanical properties and microhardness of the different welding joint area, it is found that the microstructure is more uniform, the mechanical properties are better and the microhardness is slightly higher at the position with lower welding heat input.