Abstract: Based on Mises yielding condition theory, incremental theory and the assumption that the material is ideal elastoplastic, this paper obtained stress components of thinwalled straight bar with close section under tension, compression and torsion combined deformation by using nondimensional method. When thinwalled straight bar with close section is subjected to tension, compression and torsion combined deformation, and that the materials get to the plasticity stage, two correlative ordinary differential equations in respect with the compression and torsion subjected on the thinwalled straight bar with close section are obtained based on the theoretical analysis. Stress components can be obtained with analytical solution by solving the ordinary differential equation. Those will lay the foundation for the studies on buckling and stability of thinwalled straight bar with close and open section.