Abstract: In order to study the feature of welding residual stress distribution and distortion induced by electro slag welding (ESW), a computational approach was developed to predict welding temperature field, welding residual stress and distortion using MSC.Marc software. In the proposed approach, a new heat source named full ellipsoid volumetric heat source with uniform density was developed to model heat input produced by ESW. The "birth and death" element technique was used to simulate the formation of weld bead. The welding residual stress distribution and deformation in the box column plate and diaphragm were calculated. Meanwhile, the transverse shrinkage and angular distortion were measured by experiment. The results show that the numerical results are in a good agreement with the measured data, and the effectiveness of the computational approach was verified. In addition, the general features of welding residual stress distribution in the ESW joint was numerically investigated.