Based on the thermal elastoplastic finite element theory and Abaqus analysis software,the residual stress and deformation of fillet joint after welding are analyzed. The segmented moving heat source model is adopted and the heat source subroutine is developed by using Fortran language. The numerical simulation analysis of the welding temperature field,residual stress and deformation of the fillet joint is carried out by means of straight through welding and backstep welding respectively. The results show that the transverse deformation is the main deformation of the fillet joint;the residual stress at the weld end of the fillet joint is compressive stress,while the residual stress in the middle part is tensile stress;the transv-erse residual stress is obviously weakened by backstep welding,which can effectively reduce the deformation and stress after welding.