Abstract: The geometric nonlinear analysis of curved beams with thin-walled open sections is performed. With the updated Lagraign formulation, a Hermitian polynomial is adopted to describe the displacement field. Warping degree of freedom and curvature effects are taken into consideration to simulate the structural behavior of curved thin-walled beams with open sections. In this formulation, all displacement parameters are defined at centroid axis so that the couple terms of bending and torsion are added to elastic strain energy. The improved arc-length method is adopted to trace the nonlinear load-deflection path. Numerical examples are presented to illustrate the validity and the accuracy of the proposed numerical approach. It is found that warping deformation is not negligible in the analysis of thin-walled beams.