Abstract: While 5A03 welding wires were used to welding 5A02 antirust aluminum alloy pipes, 5A03 welding wires were mixed with 2A10 aluminum wires. In order not to damage the pipes, the inner welds of the pipes were polished in situ to form powder, and then ICP-AES spectroscopy was used to analyze the chemical composition of the powder. The mass fraction of Cu element in the powder was used as a characteristic element to distinguish whether 5A03 welding wires were mixed with 2A10 aluminum wires, and the changing law of the mass fraction of Cu element was established for different pipe diameters. The results show that the larger the pipe diameter is, the smaller the mass fraction of Cu element in the powder is. Under the same pipe diameter, the mass fraction of Cu in the powder gradually increases with the percentage of 2A10 wires rising. For ϕ42~60 mm aluminum pipes, when the mass fraction of Cu in the weld powder is greater than 0.06%, it can be judged that mixing occurs to at least one anchor point in the welding process; when the mass fraction of Cu is greater than 2%, it can be judged that all the welding wires are 2A10 aluminum wires.