Abstract: In order to evaluate the present pre-twist process of the tank torsional axis, by elastic-plastic finite element analysis method, a torsional axis' pre-twist process and limited loaded process were simulated. The stress states were presented under three kinds of case. The results indicate that the elastic operating stress range of a torsional axis is extended greatly by pre-twist process and the main reason lies on surface residual stress. Besides, the pre-twist process used presently don't make use of materials' potential ability adequately.