Fiber-reinforced composite materials often exhibit nonlinear stress-strain behavior under the combined tension-compression and shear with respect to the transverse direction to the fiber. This paper focuses on the mechanical description of the nonlinear inelastic behavior of CFRP. In order to obtain fundamental data to elucidate the inelastic behaviors of the composite, quasi-static failure tests were firstly performed on unidirectional and symmetric angle-ply laminate tubes with different fiber orientations. Then, the flow rules proposed by Chow et al. were modified and developed to describe the non-linear mechanical behavior of symmetric angle-ply laminates under multi-axial loading. Comparison between the experimental data and the theoretical predictions showed that the proposed theory can appropriately describe the inelastic behavior of CFRP.