The shift fork shaft is an important component in manual transmission, automatic manual transmission and dual-clutch transmission to connect the fork and adjust gear engagement. To study the relationship among welding deformation, residual stress and welding process parameters during plasma welding of shift fork shaft, based on ABAQUS simulation software, the temperature-displacement coupled finite element calculation method was adopted and double ellipsoidal heat source model was selected to numerically simulate the stress field, deformation and temperature field of the welded plate and shift fork shaft. The optimization of the welding process of shift fork shaft was completed, and the reliability of the optimized model was verified through simulation and experiments. The results show that welding deformation is decreased with the increase in welding speed. The welding deformation is relatively small at welding speed of 2.5–3.0 mm/s and is increased with the increase in welding current. The welding residual stress does not show a significant variation law with welding current and welding speed, but the peak values are distributed around 560 MPa, which is smaller than the tensile strength of the fork shaft (650 MPa), and there is a local stress concentration phenomenon. Overall, residual stress is mainly distributed at both ends of the weld seam, and deformation mainly occurs at the weld plate. The optimized model has a more balanced peak temperature of the two weld heat sources, and local welding residual stress and deformation slightly decrease. Therefore, simulation and experimental results can provide theoretical guidance for the control of welding quality in actual production process.