A mathematical model of drop-impact erosion (wear) of steam turbine working blades by a single drop is proposed. By means of the theory of elasticity and computer programs Mathcad and Abacus the stress state of the input edge material, arising due to impacts of steam particles with a velocity of 150…600 m/s, has been calculated. The values of load and distance from the surface at which plastic deformation began were determined. The validity of the proposed model was confirmed by the experimental data of the authors, as a result of the conducted research on 3 stages of the characteristic curve of metal drop-impact wear in time and the forms of the eroded surface corresponding to these stages.