It is essential to predict precisely the welding deformation of hull structures at assembly stage, to built accurately ship blocks and to increase productivity through mechanization/automation effectively. At a first step of the studies, a practical system applied for production engineering was proposed to simulate in-plane deformation of one side automatic welding of the panel, with an analytical model using finite element method solving unsteady heat conduction problem and thermal elastic-plastic behavior. Some parametric studies were carried out using this numerical simulation system and also experimental measurements : (1) The distribution of the shrinkage across the butt weld is affected mainly by residual stresses due to tack welding, fitting of tab plate and so on. (2) Some countermeasures to prevent end cracking in one side welding, such as local heating in the vicinity of the plate edge and changing of welding sequence, affect also the distribution of the shrinkage, while pitch of tack weld beads, type of tab plate and root gap have less effect.