An approach to the structure buckling reliability analysis for the underwater super-speed supercavitating vehicle is proposed in this paper. The circular ribbed part-cabin of the vehicle is simplified as the thin cylindrical shell with variable thickness. The critical buckling load coefficient of the thin cylindrical shell is solved by using semi-analytical FEM (finite element method). The structure buckling reliability index is obtained by SFEM (Stochastic Finite Element Method) combining Limit Step Length Iteration Method. A numerical example is given to analyze influences of the number of circular ribs, the coefficient of variation of elastic modulus and the coefficient of variation of the thickness of the thin shell on the structure buckling reliability index.