Abstract：On July 13，2003，a foundation rock landslide with total volume of about 2.04´107 m3 happened in Qianjiangping on the left bank of Qinggan River in Zigui County located in the Three Gorges Reservoir area. Intensive attention has been aroused for the geologic features and startup mechanism of the landslide because it located in the Three Gorges Reservoir area and happened in the time no more than 2 weeks after the storage of the Three Gorges Reservoir up to 135 m elevation. On the basis of field investigation on the general geological conditions and its mechanical parameters of the actual landslide，and with advantages of real time variable employment and large discontinuous deformation simulation in the method of discontinuous deformation analysis(DDA)，the startup criterion for a landslide using DDA numerical modeling has been studied；and the numerical simulation of the startup and whole failure process of the landslide has been carried out by use of DDA method. It is shown that the main reason of Qianjiangping landslide is the reduction of mechanical parameters of controlled sliding surfaces in the landslide body resulted from rainfall and rise of reservoir water level. The landslide belongs to thrust load caused landslide. Compared to the actual process characteristics of the Qiangjiangping landslide，the maximum landslide velocity，and the maximum slide distance are quite reasonable and acceptable. The total duration of the landslide obtained by DDA modelling is about 40 s. In addition，the methods adopted in this paper supply a new approach for stability study of landslide or other geotechnical engineering.
