Abstract: The relationship between the normal contact force and normal indentation for the process of plastic loading and elastic unloading is studied on the basis of theoretical analysis. The approach velocity and rebound velocity have been deduced theoretically. A coefficient of indentation is introduced to describe the unloaded curvature of material. The unloaded material curvature and loaded material curvature has been discussed. The dynamic behavior of a circular plate impacting on a plane block is investigated experimentally. The approach and rebound velocities during the impacting process are measured using a high-speed video camera. It is found that the approach velocities have more influence on the coefficient of restitution. The calculated data using the modified coefficient of indentation had a good fit to the experimental data about coefficient of restitution.