Restrained torsion analysis of open thin-walled beam is presented in this paper. A finite element model is developed. The element is based on the first-order torsion theory, which accounts for the warping deformation and shear deformation due to restrained torsion. The interpolation functions of total rotation and twist rate of free warping rotation of cross section are constructed respectively by using the relationship between these two rotations. Numerical example is illustrated to validate the current approach and the results of the current theory are compared with those obtained from classical Vlasov theory and first-order torsion theory.