Abstract: The Middle Triassic reefoid continental margin of Guizhou Province can be taken as the boundary between the shelf and the back-arc basin, where the carbonate sediment of the debris flows developed. Debris flows could be developed by fracturing and collapsing of reef-margin rocks due to the over pressure of pore-fluids and the suspension of clay-water matrices. As large fragments could not be suspended completely by the cohesive force and the buoyancy of the matrices, they had to roll, slide and bounce intermittently. The debris flows are distributed in the channel on the slop which stretched perpendicular to the strike of the reef margin. Since the channels are shallow and wide, there are slight washing surfaces around the lower limits of the infilling conglometates.