Abstract: Groundwater in karst aquifers has an important effect on the large landslides frequently occurring in the karst mountain areas in southwest China. The storage rule of karst groundwater and its impact model on landslide disasters have become a scientific problem to be studied urgently. At 14:00 on June 28, 2010, a huge landslide disaster occurred at Dazhai near Gangwu Town in Guanling County of Guizhou Province, resulting in dozens of deaths and a large number of residential damage.This paper takes the Dazhai landslide as an example, and the field investigations, combining with hydrodynamic field analysis, hydrochemical analysis, rainstorm data analysis and comprehensive analysis are carried out. The research results show that (1) the underground watershed of the Dazhai landslide area is divided, and the area of limestone and clastic-rock affecting the Dazhai landslide is delineated as 0.93 and 0.30 km2, respectively; (2) The heavy rain on the day of the landslide mainly occurred at 6:00—12:00, and it is considered that the karst conduit water in the trailing edge area plays a major role in controlling the start of the Dazhai landslide 2 hours after the heavy rain. (3) After the recharge of once-in-100-years heavy precipitation, the high-pressure hydrodynamic field was formed respectively in clastic-rocks and trailing edge limestones of the landslide area. Under the combined action of the two hydrodynamic fields (bedrock fissure water and karst conduit water) and the gravity of the rock-layer, rock formation instability on potentially weak structural surfaces was caused and the formation of this landslide was eventually occured.This paper establishes the landslide impact model of the compound hydrodynamic field of bedrock fissure water and karst conduit water, and may provide a method of coupling the compound hydrodynamic field.