///Dangerous rock masses pose a great threat to traffic and residential security in southwestern region of china, especially, the “5.12” earthquake in Sichuan Province had caused the collapse of instable rock masses which was formed originally, at the same time, a large number of new dangerous rock masses had been appeared. A dangerous rockmass in Wenchuan County of the province could be divided for three failure modes: rip-slip failure mode, whole shear fall failure mode and bending-rip-dumping failure mode. When dangerous rockmass was instable, the falling rockmass would be bouncing, rolling and sliding along the slope.