Abstract：By the site investigation and exploration of engineering geology，physico-mechanical tests in laboratory and field，adopting the analytic mathematic statistics and unbalanced-thrust method，with the concrete engineering practice of debris landslide，the general physico-mechanical characteristic and permeability of debris landslide，the influence of its groundwater pipe network drainage system(GPNDS) on its stability，and the action mechanisms of its instability and failure are researched and analyzed. The research results are as follows. First，the influences of the contents of block and broken stone grain-grade，and fine earth mainly made up of silt and clay grain on debris permeability coefficient are the biggest and most remarkable. Second，debris permeability coefficient increases and decreases in natural exponent，respectively，with its grain-grade contents of block，broken stone and gravel，and the fine earth with grain size less than 0.1 mm. Third，the GPNDS of the debris landslide takes crucial action on natural slope stability. Fourth，when the GPNDS of the debris landslide is destroyed and blocked，groundwater level will obviously rise to make the pore water pressure of potential slide plane and down-sliding force clearly increase，which will make the slope stability coefficient descend obviously，even result in slope instability，disintegration and failure to some extent.
