Abstract: The welding temperature field in T-joint P355NL1 steel plates was measured by using an infrared thermography, and the welding thermal cycle curves were obtained, which have good agreement with the simulation results.The residual stress in T-joint plates was measured by blind-hole method after MAG welding, TIG dressing and heat treatment.The residual stress in T-joint plates was calculated according to the simulated welding temperature field, and the calculated results correspond with the experiment results.The results showed that the method of TIG dressing could lower the residual stress in seam center area to some extent, but the residual stress in remelted area increased.However, the overall heat treatment can effectively relieve residual stress caused by TIG dressing, but there is still partial residual stress in joint.