In this study, a computer program is developed for analyzing the elasto-plastic dynamic behaviors of the plates subjected to line-loading by a low-velocity impactor. The equilibrium equation associated with the Hertzian contact law is formulated to evaluate the transient dynamic behavior of the impacted plates. Compared with an elastic analysis, the effects of material plasticity are considered. Consequently, in the case of elasto-plastic analysis, impulse decreases, displacements increase and contact duration time is longer than that of the elastic case for the same plate structures. And the time variation of the impacting load is not significant due to the plasticity except at the beginning of impact duration, and the induced stresses of plate are more realistic.