Abstract: In order to reduce the residual stress after repair welding of steam turbine cylinder in service,the residual stress distribution of defective thick-wall steel castings after multi-layer and multi pass repair welding was simulated by the birth and death element technology in ABAQUS. Under the condition of ensuring the accuracy,the segmented heat source model was adopted to study the thermal cycle curve of repair welding process and the distribution of welding residual stress in the three-dimensional model of thick-wall steel casting. The effects of different preheating temperature and different layer thickness on the residual stress distribution in the repair welding area were analyzed,and the more reasonable preheating temperature range and the corresponding welding repair method matching the layer thickness and the number of layers were obtained.