In this paper,the mechanical properties of 6005A aluminum alloy profiles are tested and the microstructure of extruded weld and base material is observed to determine the weak position of aluminum alloy profiles and discuss the difference between the mechanical properties and microstructure in the weak position and its causes. The results show that the microstructure of the extruded weld and the base material is Mg,2,Si evenly distributed in the aluminum matrix,but the Mg,2,Si in the extruded weld is thicker and more disorderly. The grain shape of the extruded weld is mainly strip grain and fine equiaxed grain,and the average grain size is 15.5 μm.In the process of hot extrusion,the non-uniformity of grain size in the extruded weld increases,and the coordination between grains becomes worse during deformation. Cracks are easy to occur in tensile process,which makes the material strength decrease and becomes the weak position of aluminum alloy profile. The average hardness of 6005A aluminum alloy profile is88.176 HBW,the minimum value is 81.7 HBW,and the minimum value appears in the extruded weld. The sample position 6 has the minimum elongation after fracture（4.5%）,and it is judged that the sample position 6 is the weakest position of the profile.