Abstract: Liner shell made of superelastic Mylar polymer film was constrained by outside steel cylinder. Boundary conditions were provided by stiff-rings on both ends. The shell was under uniform lateral pressure loaded by pumped air. The buckling process was observed and the critical buckling loads were measured, which were in good agreement with FEM results. By imposing initial defect and changing the length of the shell, the relationship between the critical loads and the initial imperfections, critical loads and L/R were studied. The results indicate that the confined buckling critical load of cylindrical liner shells was much higher than buckling critical load of same shells without outside constraints.