Abstract: A large scale of mountain collapse occurred in Jiwei mountain, Wulong county. Chongqing City on June 5, 2009. Its volume is of 5106 m3. The limestone rock mass was cut by a set of discontinuities into a shape of building blocks, and slipped down along a low angle dip inter-bedded shale plane. The high speed moving mass blocked the valley. The valley was 200 m wide and 50 deep. The debris accumulated in the valley. It is of 30 m thick in general and 2200 m long. The debris destroyed 12 houses, killed 10 people, buried 64 people, and injured 8 people. Based on site investigation, the remote sensing, three dimension laser scanning technologies, this paper provides a detailed description on the landslide. It then gives the analysis on the mechanism of the landslide. The results show that the causes of the Jiweishan landslide are complex geological settings, long term loading stress, karst effect and the underground mining activities. The triggering factor is the failure of a relatively small key rock block in front of the main landslide body. The key block had been functioned as a barrier or shear key to make the main landslide body stable. There will be a big attribution if such case can be studied further. It can provide the significant experience on dealing with this kind of landslide and how to provide advice on early warning and remediation project on similar cases in south western China under such complex geological setting.