Abstract: A nondestructive experimental method is provided for determining critical loads of shell structures under external pressure.It is a step-by-step method using normal deflection of shell structures as control variation.The nondestructive buckling tests on 9 cylindrical panels made of LY12-CZ aluminum alloy with circumferential Ω-stiffeners and internal panels of 3rd to 6th oil boxes in an airplane fuselage-were completed with the presented method.The critical pressures of shells-were exactly determined.A preliminary investigation on influence of the circumferential restraint on the buckling loads of stiffened cylindrical panels has been carried out.The test results show that the nondestructive buckling experimental method is a success.