Abstract: In order to control and study the welding deformation of the low temperature superconducting magnet supported by fusion reactor. In this paper, the thermal elastic plastic finite element analysis of 3 mm 316 LN for TIG butt welding test and welding deformation measurement were carried out. The results indicated that the deviation of the welding temperature field from the measured values was less than 20 %. Based on this, the welding deformation and residual stress of the deformed support structure were studied. It was found that the residual stress rebalance after the release of the jigs was the main reason for the large deformation.Therefore, it was shown that thermal elastic plastic finite element analysis could be used to predict welding deformation of 316 LN complex components.