Abstract: At present,there are many researches on the influence of welding parameters,welding sequence and constraint conditions on welding deformation,but there are few scientific researches on the influence of structural stiffness on welding deformation. In this study,the threedimensional thermal elastic-plastic finite element analysis of T-joint was carried out. Four components of inherent strain were extracted using inverse analytic method in the results of thermal elastic-plastic FEM. The inherent strain was proved to be reasonable by the experiment. Based on the inherent strain theory,the elastic finite element method was used to predict the deformation of thin-walled box beam. Finally,the influences of web space and height on welding deformation were studied quantitatively. Numerical results showed that the welding deformation of the thin-walled box beam was reduced with the increase of the web space in a certain range,and a linear function was established. The welding deformation was also reduced with the increase of the web height in a certain range,and a quadratic function was established.