Abstract: Collapse is one of the major secondary geological disasters induced by Wenchuan earthquake on May 12th,2008.Based on many on-site investigations of collapse bodies in disaster areas,the movement process of unstable rock masses is divided into three stages of free-fall,bouncing,and rolling.Mathematical models of the three stages are established separately.Yangjiatai collapse body in Jiuzhaigou is taken as an example.Its velocity of unstable rock masses,rolling distance,and impact force are calculated.The models can provide a basis for the treatment design of the collapse bodies in the disaster reconstruction process.