It has been widely studied about the final residual stress and deformation in multipass welding of thick weldments. But there is a lack of a clear understanding of the interrelationship of interpass stress and deformation during multipass welding. In this study, a three dimension numerical model of a sixteen-pass double V-groove welded joint with 50 mm plate is developed to compute the stress field and deformation by using multiple CPU parallel processing technology. The following factors such as the non-linear of temperature, heat radiation, filling of material step by step and so on are considered. Distribution and evolution law of welding stress in the transverse and longitudinal section is analyzed in this paper, and the interpass stresses are studied also. At the same time the evolution course of angular deformation amount is analyzed, and the experimental results show that the calculated results accord with the measured results of angular deformation. It has been widely studied about the final residual stress and deformation in multipass welding of thick weldments. But there is a lack of a clear understanding of the interrelationship of interpass stress and deformation during multipass welding. In this study, a three dimensional numerical model of a sixteen-pass double V-groove welded joint with 50 mm plate is developed to compute the stress field and deformation by multiple CPU parallel processing technology. The following factors such as the non-linear of temperature, heat radiation, filling of material step by step and so on are considered. Distribution and evolution law of welding stress in the transverse and longitudinal section is analyzed in this paper, and the interpass stresses are studied in. the experimental results show that the calculated results accord with the measured results of angular deformation.