<p>The paper presents a numerical study of the vibration-stressed state of the vaned disc of the last stage of a powerful K-1000-60/3000 low-pressure cylinder steam turbine under the action of a harmonic force load from the steam flow. The vaned disc is considered a disc-blade system with disturbed cyclic symmetry, resulting from local damage to the upper third of the blades due to erosive wear. It is shown that local changes in geometry lead to a disturbance in the natural frequencies of vibrations and a change in the level of equivalent stresses in both damaged and adjacent blades under the action of a static load on the bladed disc from the action of centrifugal forces and steam flow. Based on the analysis of the disc-blade system’s natural modes and frequencies of vibration, it was found that low-frequency modes are insensitive to local geometric changes. In contrast, in the high-frequency range, the relative deviations in the natural frequencies of damaged blades range from 0.6% to 0.8%. The results obtained allow a quantitative assessment of the influence of local erosion damage on the spectrum of natural frequencies and the nature of vibration localization in the disc–blade system. They can be used to assess the residual life and vibration reliability of working blades, as well as to monitor their technical condition.</p>