Supercavitating vehicles which cruise at a certain depth with high underwater velocity undergo high longitudinal force and circumferential pressure caused by ventilated cavity. The combination loads may cause structure buckling. Critical buckling loads coefficient of thin cylindrical shell with stiffened rings is obtained by semi-analytical FEM. The uncertainty of structural own parameters and ventilated cavitation number is described by interval sets, and then computational steps of COA for calculating buckling non-probabilistic reliability index (BNRI) are presented. It is analyzed that variety of each interval variable width, number and configuration of rings influence on the variety of BNRI in this paper.