Abstract: Based on thermal-elastic-plastic theory, a three-dimensional numerical analysis model for multi-layer and multi-pass homogenous repair welding residual stress of P91 steel was established by considering solid phase transformation. The heat input of shielded metal arc welding was described by a double ellipsoid heat source model. Based on the established model, SYSWELD finite element analysis software was used to simulate and calculate the temperature field, microstructure distribution and post-welding residual stress in multilayer and multipass repair welding of P91 steel, and to study its distribution characteristics. The results showed that the solid-state phase transformation could make the transverse stress show more obvious compressive stress at the last weld, and the compressive stress value was-93 MPa. The longitudinal stress was characterized by the staggered distribution of tensile stress and compressive stress on the near surface. The longitudinal compressive stress of the last weld was larger and the stress value was-155 MPa.