Abstract: The 19. 05 mm thick Invar steel plates were taken as the research object,which were joined by multi-layer weave bead welding experiments. The temperature field model is established by the finite element method. The transient temperature field and the welding thermal cycle curve are analyzed,and the change process of the whole temperature field of the sample during the welding process is obtained. The results show that the weld pool size becomes larger because of the increase of welding time and the slow welding speed. The thermal cycle curve near the center of heat source changes drastically,and the thermal cycle curve away from the center of heat source changes gently. The thermal cycling curve of straight welding is a smooth curve,and the thermal cycling curve of swing welding is a series of uniform broken lines. The frequency of the broken line is consistent with the frequency of the welding torch swing.