Abstract: As one of the most serious secondary mountain hazards of Wenchuan 8.0 Earthquake, the rock-fall is very hard to treat for its randomness and unpredictability. Based on the HERTZ theory, the characteristics of normal impact of rock-fall is studied by utilizing the finite element analysis software, ABAQUS. The analysis considers the elastic-plastic properties of slope materials and simplifies the impact as a mechanical problem of a sphere into a half-space loaded normally. Then the effect of impact velocity and radius of rock-fall on the dynamical response of slope is analyzed. The result shows that the values calculated by elastic-plastic theory agree well with the numerical simulations, while the results given by perfect elastic impact theory are much larger than the actual one, which indicates that the engineering design of rock-sheds based on elastic plastic theory would be more reasonable.