Abstract: A round-robin research on multipass butt welding of 7B05 Al-alloy plate was carried out to provide a reliable numerical simulation method for the complex welded structure. Welding heat source model and softening model were founded. The 3D thermal and mechanical analyses were carried out to simulate welding process. The simulated results were compared with the measured results to validate the reliability of welding numerical simulation method. The results show that the predicted temperature field, residual stresses and welding distortion have a good agreement with the measured results, which indicates the accuracy of the numerical simulation method.