To predict the effect of phase transformation plastic stress and microstructure transformation on the hardfacing effect in the process of repairing the failed roll by submerged arc welding, this paper calculates the temperature dependent physical parameters of hardfacing material by CALPHAD (calculation of phase diagram), and numerically calculates the transient temperature field, martensite phase composition and transformation induced plasticity (TRIP) stress evolution process of roll submerged arc welding process based on COMSOL multi physical field coupling platform. The results show that the temperature field distribution and martensitic transformation are sensitive to the heat transfer rate. Compared with the hardfacing layer, the heat transfer of the weld near the substrate side is faster, resulting in faster martensitic transformation, and the transformation plastic stress value shows a larger broadband distribution. During the cooling process, the stress value of HAZ decreases slowly due to martensitic transformation. The maximum residual stress after cooling is 376 MPa, and the martensite phase accounts for 94%. The metallographic structure of roll hardfacing slice is observed by Zeiss-?igma HD field emission scanning electron microscope, and the accuracy of the model is verified. It can be concluded that the numerical simulation method can accurately predict the plastic stress change and microstructure evolution law in the process of submerged arc welding, which provides an effective way and method to reduce and eliminate the residual stress, and offers a theoretical basis for preventing the defects of roll hardfacing layer.