Abstract: A three-dimensional thermal, metallurgical and mechanical finite element model was established by using SYSWELD software for the multi-pass of T-joint in high strength steel, considering phase transformation, to simulate and analyze the temperature field during welding process, residual stress and the distortion. And the simulated results were compared with the test results. The effect of phase transformation on welding distortion was also studied. The results show that multi-pass welding process parameters can be optimized using thermal cycling curves. Stresses were longitudinal and transverse tensile stresses in and near the welding line, and longitudinal compressive stresses and transverse tensile stresses away from the welding line, and the stress in the welding line was less than that near the welding line. The model can accurately predict the welding residual stresses and the results coincided with experiment. Distortions with and without phase transformation were consistent, and the phase transformation had a negligible effect on the distortion.