Abstract: The genetic algorithm method was proposed.The box structure's nonlinear three-dimension optimization simulation model was eslablished based on thermo-mechanical coupling algorithm, and the objective function of welding distortion has been utilized to determine an optimal welding sequence by optimization of simulation. This genetic algorithm method combining with thermo-mechanical nonlinear finite element model was verified by comparison with available experimental data. By choosing the appropriate objective function for the considered case, an optimum welding sequence was determined by the genetic algorithm.This study indicates that presented new method has important practical application for designing the welding technical parameters.