Abstract: The elastic torsional deformation of self-balanced torsion bar is one of the most crucial issues because its torsional energy has an important influence on the reliability of an Oxygen Top-Blown Convertor. Based on the elementary cylindrical torsion theory, the analytical solution of the torsional deformation of a torsion bar with circular, cone and fillet variable cross-sections were derived. Taking a self-balanced torsion bar in a 150-ton convertor as an example, the correctness of the analytical solution was verified by the numerical result simulated by the finite element software ANSYS. The calculation result and the numerical result have good agreement. The practical application of the self-balanced torsion bar in a 150-ton convertor shows that the two methods are valid in the design. But the analytical method is more simple and convenient than the finite element method, more suitable for engineering applications.