Abstract: A huge high-speed landslide occurred in Wenjiagou of Qingping township, Mianzhu city, during the 5.12 Wenchuan earthquake. By systematical analysis of the geologic conditions and the landslide movement characteristics, the initiation breaking and instability occurring model is proposed regarding the effects of earthquake and landslide ground vibration. Then, the processes of rock mass movement is classified as four stages which include ejecting, flying and scraping, collision and direction altering, stopping and accumulating stages. Considering the earthquake and landslide ground shaking forces, the total force direction is 285° and approximately equals to the landslide initiation direction. Furthermore, the average velocity and time corresponding with the movement mass in each stage are calculated. The average velocity is 115.64 m·s^-1, 69.38 m·s^-1, 41.6 m·s^-1, 20.8 m·s^-1 and the respective sub-total time is 11.8 s, 8.6 s, 24.0 s, 48.1 s for the ejecting to stopping and accumulating stages, respectively. The total time of the landslide movement is 92.5 s, almost same as more than 1 minute estimated by the survival inhabitants. The results show that the main reason that cause Wenjiagou landslide to move with high speed is the effect of ejecting and flying, which transfer the gravitational potential energy to kinetic energy completely.