Abstract: The ANSYS software and substructure method were used to optimize welding procedure to accurately predict the distribution of welding temperature and residual stress in largescale pipe of SA508-3 steel for nuclear power. Comparing the simulated and experimental results,it was found that the computation method could successfully simulate the real welding process,and the calculated values agreed well with the measured ones. The thermal cycle curves of all nodes on the weld were similar,the simulated width of heat affected zone was about 4 mm. The residual stress values of arbitrary nodes in the weld centerline on outer surface of pipe were close to each other,however, axial compressive stress only occurred near the weld centerline on outer surface of pipe,tensile stress appeared in other areas with higher value in the circular direction. The pipe had a concave residual deformation after welding. The results could provide theoretical guidance for analyzing the residual stresses in girth welding of large scale pipe.