The paper presents results of a numerical and experimental analysis of post-critical state of a thin-walled channel-section simply supported beam under axial compression. The beam was made of carbon-epoxy symmetrical composite prepared with a pre-preg technology using 8 layers of unidirectional band. The material used was a composite of epoxy matrix reinforced with carbon fiber (system HexPly M12, Hexcel). The M12 system is used above all in aircraft structures. It exhibits high fatigue durability and good maintenance properties at relatively low specific gravity. The research was lead as the FEM numerical analyses and experimental tests in post-buckling and limit states, as well. Experimental studies were conducted to confirm results obtained from numerical calculations, which was performed using the ABAQUS® software.