Abstract: Permanent dent defects induced by the impact of high falling objects on ship hull decks exert a significant influence on the ultimate strength of deck stiffened plates. Most existing studies apply simplified impact-induced dents as additional initial deformation defects to stiffened plates models, followed by nonlinear finite element analysis for ultimate strength evaluation. However, these approaches fail to account for the actual impact process of high falling objects, the realistic post-impact damage morphology, and residual stresses. In this study, the explicit dynamic method was first adopted, with the Cowper-Symonds material constitutive model employed to simulate the impact process of high falling objects on a deck stiffened plate, thereby obtaining the plastic damage characteristics and residual stresses distribution of the stiffened plate after impact. Subsequently, nonlinear finite element analysis was conducted to evaluate the ultimate strength of the stiffened plate with impact-induced damage. Specifically, the damage formation process of the stiffened plate under impact, as well as the effects of impact mass, impact position, and dent-induced residual stresses on the ultimate strength, were discussed in detail. The results indicate that the degree of permanent damage deformation varies with different impact positions and tends to aggravate with the increase of falling object mass. Considering the plastic deformation and residual stresses caused by dent defects reduces the ultimate strength of the stiffened plate, which decreases with the increase of falling object mass, with a maximum reduction of 29.8% in the most severe case.