Abstract: The Dazhai event happened at Jun 28, 2010 in Guling county of Guizhou province of China.It is a sliding in rockfall and debris events(volume is about 78.8104m3),and an oversize geological disaster(the number of missing and death is 99 residents).It is taken for that rockmass breakdown results mainly from dry building block structure in fissured rockmass in internality of Dazhai slope by through field looking into collapse phenomena.That sustaining water wedge pressure acts on the crown cracks by pouring rainwater from extreme rainstorm,process rainfall reach to 237mm,is main external triggering factor which result in slope rockmass loosening,toppling,rotating and falling finally.The grain size distribution of debris(crushed stone)flow is to change small gradually from rockfall headstream to stop outlet of the ditch.Still,its impact height is to knock down and strike velocity is to be decrease gradually.The total process of the debris(crushed stone)flow displays that multilevel of potential energy transform into same number of kinetic energy and accordingly occur in multi-strike paths.Based on the law of conservation of energy,maximum velocity in each strike path is calculated and obtain that first stage belongs to rockfall and slip in high velocity(V1=24.25m s-1),others are debris(crushed stone)flows.It is not discovered that direct evidences of the event exist related with natural earthquakes,Guangzhao reservoir induced seismic activity and historic coal mining in the region.Moreover,it may be predicted that possibility of debris flow happening again is existent because there are unstable rockmasses in collapse area and dammed ponds in the debris deposits of 3~5m in diameter that show capacity for to drainage to be not enough in open space of crushed stones.