Abstract: The numerical simulation of welding deformation of upper plate structure for large-scale crane box beam was conducted using the thermo elastic-plastic method.Analysis model was established to quantitatively describe the effects of welding sequence for both longitudinal rib to upper plate and transverse rib to upper plate on welding deformation.The optimal welding sequence of the whole structure was obtained by the term of the "and" relation.The simulation value of deformation under the optimal welding sequence was contrast to measured value to show the better agreement for two values.The deformation of the optimal sequence and the worst sequence was 15.12 mm and 28.47 mm, respectively.