In order to provide effective guarantee for the prediction of residual stress and deformation after welding process of large-sized aluminum alloy structures, temperature field and thermal efficiency during double-sided multi-layer TIG welding of aluminum alloy was studied. By integratedly considering temperature-depended material properties, convection, radiation, filling rate of solders, et al, numerical analysis about the form of molten pool and temperature field was given. Element birth and death technique was taken during the simulation. Double-sided multi-layer TIG welding experiment was carried out and sample of cross section of weld seam after welding was prepared. By trying different thermal efficiency for calculation, simulation result consistent with experimental result was obtained finally, making the present thermal efficiency as the aim result for study. Confirmation was given by comparing temperature value from experiment with simulation one.