Abstract: A mathematical method of Using the Code of direct question to Solve inverse question is described. With this method on the basis of free-boundary toroidal MHD equilibrium Code SWEQU^[1] We developed our own Code SWSTAB, Which can be used to calculate vertical instability of Tokamak plasma with noncircular cross section. Practical examples show that Some physical results are obtained by this method more easily than by others.

Key words: A free-boundary toroidal MHD equilibrium code, Vertical instability of Tokamak plasma with noncircular cross section