Abstract：In the design of rock-fall protection project，the proper location and reasonable intercepting height of the intercepting system are most important factors，which directly are concerned with success or failure of the system. There are many factors which can influence the system，but among them the stone motion track on slope plays a key role. Based on the elasto plastic contact theories，the calculation models of restitution coefficient both in normal and tangential impacting directions are studied. Then the fundamental kinematical equation is applied to studying the stone motion characteristics，and the related formulas are deduced. At last，by calculating and analyzing a specific example，the theory is proven to be reasonable.
