///The Dazhai event happened on June 28, 2010 in Guling County of Guizhou Province. Field inspection of the collapse phenomena indicated that the rockmass broken down was mainly due to the “dry building block structure” in fissured rockmass in internality of Dazhai slope. The sustaining “water wedge” pressure acts on the crown cracks by pouring rainwater from extreme rainstorm was the main external triggering factor. The rainfall was about 237 mm. These factors resulted in the loosening, toppling, rotating and falling finally of the slope rock mass. The grain size distribution of debris (crushed stone) flow changed from larger to smaller sizes gradually from the rock fall headstream to the deposition outlet of the ditch. Based on the law of conservation of energy, the maximum velocity in each strike path is calculated and obtained the following results. The first stage belongs to rockfall and slip in high velocity(V₁=24.25 m·s^-1).The others are debris(crushed stone)flows. Direct evidences were not found that the event was related to natural earthquakes, Guangzhao reservoir induced seismic activity and/or historic coal mining in the region.