Torsional constants of both rectangular cross section and circular cross section are induced by exact solution, and was easy to calculate since of simple shape. However, it is very difficult to calculate the torsional constant of both an arbitrary cross-section and a composite cross-section. In this study, a finite element formulation was proposed as a method to calculate the torsional constant of both an arbitrary cross-section and a composite cross-section. From the numerical study, numerical results was compared with exact solution.