The metamodeling methodology has been proposed for postbuckling simulation of stiffened composite structures that takes material degradation into account. Proposed methodology for elaboration of the fast simulation procedure for axially or torsionally loaded stiffened composite structures is based on response surface methodology (RSM) and design and analysis of computer experiments (DACE). Numerical analyses have been parametrically sampled by means of ANSYS/LS-DYNA probabilistic design toolbox extracting the load-shortening response curves. These response curves were approximated using piece-wise uniform metamodels identifying the skin and the stiffener buckling loads as well as recognising the buckling and postbuckling stiffnesses ratios. Different parametric and non parametric polynomial functions were used for metamodeling. Three stiffened panel design’s together with two closed box structure metamodels have been trained and validated with the tests performed within the COCOMAT1 project. An investigation was performed to obtain the behaviour of stiffened composite shells in the presence of predetermined degradation, in regions between the outer skin and stiffeners. Preselected degradation scenarios have been elaborated based on industrial certification requirements and the worst case scenario approach. Parametric studies over a wide range of damage sizes and sites were carried out to study the effects of the material softening parameters on overall postbuckling behaviour. The resulting design procedure provides an effective optimal design tool for preliminary study of the composite stiffened structures with the material degradation restrains in addition to optimum weight design guidelines over the buckling/postbuckling load ratios.