Abstract: The paper studied the principle of the butt welding of the aluminum alloy adopting the thermo-elasto-plastic FEM. The curves between inherent strain, that is longitudinal shrinkage value,Tendon force and traverse shrinkage value, and thermal inputting parameter (Q²/h) were obtained. On the base of learned the principle of the inherent strain the deformation of the aluminum alloy roping of the train adopting FEM of the elastic shell element by simplified welding model was predicted. The results indicate that the FKM based on the inherent strain can predict the deformation of the large welding fabrication.