Buckling and postbuckling response of thin-walled composite plates investigated experimentally and determinated analytically and numerically is compared. Real dimension specimens of composite plates weakened by cut-out subjected to uniform compression in laboratory buckling tests have been modelled in the finite element method and examined analytically based on P-w² and P-w³ methods. All results were obtained during the experimental investigations and the numerical FEM analysis of a thin-walled composite plate made of a carbon-epoxy laminate with a symmetrical eight-layer arrangement of [90/-45/45/0]_s. The instrument used for this purpose was a numerical ABAQUS^® program.