Aluminum as solder, in the flat welding process, the temperature field and the residual stress field distribution was the main problem of the study; According to the actual situation of the welding process, using the direct loading temperature method and the indirect loading temperature method , the main path of temperature field distribution curves and the residual stress field distribution were gained by 2D numerical simulation respectively; Through comparison, the indirect loading method can get more accuracy of residual stress field distribution than that of the direct loading temperature method; The above methods were useful in practical production.