Abstract: Welding temperature field was analyzed to study the affecting factors of joint formation of weaving arc narrow gap MAG welding. Under the prerequisite that the wave speed was not far higher than welding speed, effects of magnetic blow and welding thickness caused by different welding layers on the side wall were analyzed, while two heat source models for multilayer single-channel welding were established. The Comsol software was used to simulate load the heat source model and simulate the temperature field. The results showed that Gauss-generalized double ellipsoid heat source could be applied for first layer (3.6 mm) and doubled ellipsoid-generalized double ellipsoid heat source could be used for the third layer (7.8 mm). The fusion on the side wall of the simulated results approximately agreed with those of the experiments. The results were helpful for the further research about the weld formation.