Abstract: Objectives Ships navigating in extreme sea conditions are subjected to cyclic loads, which may lead to cumulative plastic deformation and degradation of the ultimate strength of stiffened panels, potentially resulting in structural failure. Methods To investigate the degradation mechanism, this study employs Digital Image Correlation (DIC) technology to conduct experimental research on the mechanical behavior of two typical stiffened panels (angle steel and T-bar) under cyclic loading. The influences of load amplitude, number of cycles, and loading sequence on the ultimate bearing capacity are systematically analyzed, revealing the intrinsic relationship between the accumulation of out-of-plane deflection and the structural ultimate strength. ResultsThe results indicate that the ultimate strength of stiffened panels degrades significantly under cyclic loading, with the angle steel stiffened panel experiencing a maximum reduction of 18.6%, while the T-bar stiffened panel demonstrates superior performance with degradation below 10%. The DIC technique effectively captures full-field deformation, providing reliable data support for analyzing the strength degradation mechanism. The findings offer a theoretical basis for the design and safety assessment of ship structures against cyclic loading.